Cleanup#1 for MDEV-34319: DECLARE TYPE .. TABLE OF .. INDEX BY

- Checking that the key expression is compatible with the INDEX BY data type
  for assignment in expressions:
    assoc_array_variable(key_expr)
    assoc_array_variable(key_expr).field

  in all contexts: SELECT, assignment target, INTO target.
  Raising an error in case it's not compatible.

- Disallowing non-constant expressions as a key,
  as the key is evaluated during the fix_fields() time.

- Disallowing stored functions as a key:
    assoc_array(stored_function())
    assoc_array(stored_function()).field

  The underlying MariaDB code is not ready to call a stored function
  during the fix_fields() time. This will be fixed in a separate MDEV.

- Removing the move Assoc_array_data's constructor.
  Using the usual constructor instead.

- Setting m_key.thread_specific and m_value.thread_specific to true
  in the Assoc_array_data constructor. This is needed to get assoc array
  element data counted by the @@session.memory_used status variable.

  Adding DBUG_ASSERTs to make sure the thread_specific flag never
  disappears in Assoc_array_data members.

- Removing my_free(item) from Field_assoc_array::element_by_key.
  It was a remainder from an earlier patch version.
  In the current patch version all Items behind an assoc array are
  created on a mem_root. It's wrong to use my_free() with them.

- Adding a helper method Field_assoc_array::assoc_tree_search()

- Fixing assoc_array_var.delete() to work as a procedure
  rather than a function. It does not need SELECT/DO any more.

- Fixing the crash in a few ctype_xxx tests, caused by the grammar change.

- Fixing compilation failure on Windows

- Adding a new method LEX::set_field_type_udt_or_typedef()
  and removing duplicate code from sql_yacc.yy

- Renaming the grammar rule field_type_all_with_composites to
  field_type_all_with_typedefs

- Removing the grammar rule assoc_array_index_types.
  Changing the grammar to "INDEX_SYM BY field_type".

  Removing the grammar rule field_type_all_with_record.
  Allow field_type_all_with_typedefs as an assoc array element.

  Catching wrong index and element data types has been moved to
  Type_handler_assoc_array::Column_definition_set_attributes().
  It raises an SQL error on things like:
  * assoc array of assoc arrays in TABLE OF
  * index by a non-supported types in INDEX BY

- Removing four methods:
  * sp_type_def_list::type_defs_add_record()
  * sp_type_def_list::type_defs_add_composite2()
  * sp_pcontext::type_defs_declare_record()
  * sp_type_def_list::type_defs_declare_composite2()
  Adding two methods instead:
  * sp_type_def_list::type_defs_add()
  * sp_pcontext::type_defs_add()
  This allows to get rid of the duplicate code detecting data type
  declarations with the same name in the same sp_pcontext frame.

- Adding new methods:
  * LEX::declare_type_assoc_array()
  * LEX::LEX::declare_type_record()
  They create a type specific sp_type_def_xxx and the call the generic
  sp_pcontext::type_defs_add().

- m_key_def.sp_prepare_create_field() inside
  Field_assoc_array::create_fields() is now called for all key data types
  (not only for integers)

- Removing the assignment of key_def->charset in
  Type_handler_assoc_array::sp_variable_declarations_finalize().
  The charset is now evaluated in m_key_def.sp_prepare_create_field().

- Fixing Item_assoc_array::get_key() to set the character set of the "key"
  to utf8mb3 instead of binary

- Fixing Field_assoc_array::copy_and_convert_key() to set the key length
  limit in terms of the character length as specified in
  INDEX BY VARCHAR(N), instead of octet length. This is needed to make
  keys with multi-byte characters work correctly.
  Also it now raises different errors depending on the reason of the
  key conversion failures:
  * ER_INVALID_CHARACTER_STRING
  * ER_CANNOT_CONVERT_CHARACTER

- Changing the prototype for Type_handler_composite::key_to_lex_cstring() to

   virtual LEX_CSTRING key_to_lex_cstring(THD *thd,
                                          const sp_rcontext_addr &var,
                                          Item **key,
                                          String *buffer) const;
   * Now it returns a LEX_CSTRING, instead of getting it as an out parameter.
   * Gets an sp_rcontext_addr instead of "name" and "def"
   * Gets a String buffer which can be used to be passed to val_str(),
     or for character set conversion purposes.

- Removing Field_assoc_array::m_key_def, as all required information
  is available from Field_assoc_array::m_key_field.
  In Field_assoc_array::create_fields turning m_key_def to a local variable
  key_def.

- Fixing Field_assoc_array::copy_and_convert_key() to follow MariaDB coding
  style: only constants can be passed by-reference, not-constants should
  be passed by-pointer.

- Adding DBUG_ASSERTs into Type_handler_assoc_array::get_item()
  and Type_handler_assoc_array::get_or_create_item() that the passed
  key in "name" is well formed according to the charset of INDEX BY.

- Changing the error ER_TOO_LONG_KEY to ER_WRONG_STRING_LENGTH.
  The former prints length limit in bytes, which is not applicable
  for INDEX BY values, because its limit is in characters.
  Also, the latter is more verbose.

- Fixing the problem that these wrong uses of an assoc array variable:

    BEGIN
      assoc_var;
      assoc_var(1);
    END;

  raised a weird error message:
    ERROR 1054 (42S22): Unknown column 'assoc_var' in '(null)'

  Now a more readable parse error is raised.

- Adding a "Duplicate key" warning for the cases when assigning
  between two assoc arrays rejects some records due to different
  collations in their INDEX BY key definitions.

- Disallow INDEX OF propagation from VARCHAR to TEXT.
  The underlying code cannot handle TEXT.
  Adding tests.

- Adding a helper class StringBufferKey to pass to val_str() when
  a key value is evaluated.
  Fixing all val_str() calls to val_str(&buffer), as the former is
  not desirable.

- Fixing a wrong use of args[0]->null_value in
  Item_func_assoc_array_exists::val_bool()

- Fixing a problem that using TABLE OF TEXT crashed the server.
  Thanks to Iqbal Hassan for the proposed patch.

- Changes in Qualified_ident:
  * Fixing the Qualified_ident constructors to get all parst as
    Lex_ident_cli_st, rather than the first part as Lex_ident_cli_st
    with the following parts Lex_ident_sys.
    This makes the code more symmetric.
  * Fixing the grammar in sql_yacc.yy accordinly.
  * Fixing the data type storing the possition in the client query
    from "const char *" to Lex_ident_cli.
  * Adding a new method Qualified_ident::is_sane().
    It allows to reduce the code side in sql_yacc.yy.
    Thanks to Iqbal Hassan for the idea.

- Replacing qs_append() to append_ulonglong() in:
  * Item_method_func::print()
  * Item_splocal_assoc_array_element::print()
  * Item_splocal_assoc_array_element_field::print()

  These methods do not use reserve()/alloc(), so calling qs_append()
  was wrong and caused a crash.

- Changing the output formats of these methods:
  * Item_splocal_assoc_array_element::print()
  * Item_splocal_assoc_array_element_field::print()
  not to print the key two times.
  Also moving the `@123` part (the variable offset) immediately
  after the variabl name and before the `[key]` part.

- Fixing a memory leak happened when trying to insert a duplicate
  key into an assoc array. Also adding a new "THD *" parameter to
  Field_assoc_array::insert_element(). Thanks to Iqbal Hassan for the fix.
  Adding a test into sp-assoc-array-ctype.test.

- In  Field_assoc_array::create_fields: m_element_field->field_name is now
  set for all element data types (not only for records).
  This fixed a wrong variable name in warnings. Adding tests.

- Adding tests:
  * Adding tests for assoc array elements in UNIONs.

  * Copying from an assoc array with a varchar key
    to an assoc array with a shorter varchar key.

  * A relatively big associative array.

  * Memory usage for x86_64.

  * Package variable as assoc array keys.

  * Character set conversion

  * TABLE OF TEXT

  * TABLE OF VARCHAR(>64k bytes) propagation to TABLE OF TEXT.

  * TEXT element fields in an array of records.

  * VARCHAR->TEXT propagation in elements in an array of records.

  * Some more tests

sql/sql_class.h

@@ -7407,28 +7407,29 @@ public:
 class Qualified_ident: public Sql_alloc
 {
 protected:
-  const char *m_cli_pos;
-  Lex_ident_sys_st m_parts[3];
+  Lex_ident_cli_st m_pos;
+  Lex_ident_sys m_parts[3];
   sp_variable *m_spvar;
   uint m_defined_parts;
 public:
   Qualified_ident(THD *thd, const Lex_ident_cli_st &a);
   Qualified_ident(THD *thd,
                   const Lex_ident_cli_st &a,
-                  const Lex_ident_sys_st &b);
+                  const Lex_ident_cli_st &b);
   Qualified_ident(THD *thd,
                   const Lex_ident_cli_st &a,
-                  const Lex_ident_sys_st &b,
-                  const Lex_ident_sys_st &c);
-  
+                  const Lex_ident_cli_st &b,
+                  const Lex_ident_cli_st &c);
+
   Qualified_ident(const Lex_ident_sys_st &a);
   /*
-    Returns the position of the first character of the identifier in
-    the client string.
+    Returns the client query fragment starting at the first character
+    of the leftmost identifier and ending at after the last character
+    of the rightmist identifier.
   */
-  const char *pos() const
+  const Lex_ident_cli_st &pos() const
   {
-    return m_cli_pos;
+    return m_pos;
   }
 
   sp_variable *spvar() const
@@ -7436,7 +7437,7 @@ public:
     return m_spvar;
   }
 
-  const Lex_ident_sys_st &part(uint i) const
+  const Lex_ident_sys &part(uint i) const
   {
     DBUG_ASSERT(i < array_elements(m_parts));
     return m_parts[i];
@@ -7447,9 +7448,23 @@ public:
     return m_defined_parts;
   }
 
-  void set_cli_pos(const char *pos)
+  /*
+    When initializing m_parts[n] in the constructor, a EOM could happen.
+    This method checks that all defined parts were initialized without error.
+  */
+  bool is_sane() const
   {
-    m_cli_pos= pos;
+    for (uint i= 0; i < m_defined_parts; i++)
+    {
+      if (m_parts[i].is_null())
+        return false; // E.g. EOM happened in the constructor
+    }
+    return true;
+  }
+
+  void set_pos(const Lex_ident_cli_st &pos)
+  {
+    m_pos= pos;
   }
   void set_spvar(sp_variable *spvar)
   {