MDEV-31340 Remove MY_COLLATION_HANDLER::strcasecmp()

This patch also fixes:
  MDEV-33050 Build-in schemas like oracle_schema are accent insensitive
  MDEV-33084 LASTVAL(t1) and LASTVAL(T1) do not work well with lower-case-table-names=0
  MDEV-33085 Tables T1 and t1 do not work well with ENGINE=CSV and lower-case-table-names=0
  MDEV-33086 SHOW OPEN TABLES IN DB1 -- is case insensitive with lower-case-table-names=0
  MDEV-33088 Cannot create triggers in the database `MYSQL`
  MDEV-33103 LOCK TABLE t1 AS t2 -- alias is not case sensitive with lower-case-table-names=0
  MDEV-33109 DROP DATABASE MYSQL -- does not drop SP with lower-case-table-names=0
  MDEV-33110 HANDLER commands are case insensitive with lower-case-table-names=0
  MDEV-33119 User is case insensitive in INFORMATION_SCHEMA.VIEWS
  MDEV-33120 System log table names are case insensitive with lower-cast-table-names=0

- Removing the virtual function strnncoll() from MY_COLLATION_HANDLER

- Adding a wrapper function CHARSET_INFO::streq(), to compare
  two strings for equality. For now it calls strnncoll() internally.
  In the future it will turn into a virtual function.

- Adding new accent sensitive case insensitive collations:
    - utf8mb4_general1400_as_ci
    - utf8mb3_general1400_as_ci
  They implement accent sensitive case insensitive comparison.
  The weight of a character is equal to the code point of its
  upper case variant. These collations use Unicode-14.0.0 casefolding data.

  The result of
     my_charset_utf8mb3_general1400_as_ci.strcoll()
  is very close to the former
     my_charset_utf8mb3_general_ci.strcasecmp()

  There is only a difference in a couple dozen rare characters, because:
    - the switch from "tolower" to "toupper" comparison, to make
      utf8mb3_general1400_as_ci closer to utf8mb3_general_ci
    - the switch from Unicode-3.0.0 to Unicode-14.0.0
  This difference should be tolarable. See the list of affected
  characters in the MDEV description.

  Note, utf8mb4_general1400_as_ci correctly handles non-BMP characters!
  Unlike utf8mb4_general_ci, it does not treat all BMP characters
  as equal.

- Adding classes representing names of the file based database objects:

    Lex_ident_db
    Lex_ident_table
    Lex_ident_trigger

  Their comparison collation depends on the underlying
  file system case sensitivity and on --lower-case-table-names
  and can be either my_charset_bin or my_charset_utf8mb3_general1400_as_ci.

- Adding classes representing names of other database objects,
  whose names have case insensitive comparison style,
  using my_charset_utf8mb3_general1400_as_ci:

  Lex_ident_column
  Lex_ident_sys_var
  Lex_ident_user_var
  Lex_ident_sp_var
  Lex_ident_ps
  Lex_ident_i_s_table
  Lex_ident_window
  Lex_ident_func
  Lex_ident_partition
  Lex_ident_with_element
  Lex_ident_rpl_filter
  Lex_ident_master_info
  Lex_ident_host
  Lex_ident_locale
  Lex_ident_plugin
  Lex_ident_engine
  Lex_ident_server
  Lex_ident_savepoint
  Lex_ident_charset
  engine_option_value::Name

- All the mentioned Lex_ident_xxx classes implement a method streq():

  if (ident1.streq(ident2))
     do_equal();

  This method works as a wrapper for CHARSET_INFO::streq().

- Changing a lot of "LEX_CSTRING name" to "Lex_ident_xxx name"
  in class members and in function/method parameters.

- Replacing all calls like
    system_charset_info->coll->strcasecmp(ident1, ident2)
  to
    ident1.streq(ident2)

- Taking advantage of the c++11 user defined literal operator
  for LEX_CSTRING (see m_strings.h) and Lex_ident_xxx (see lex_ident.h)
  data types. Use example:

  const Lex_ident_column primary_key_name= "PRIMARY"_Lex_ident_column;

  is now a shorter version of:

  const Lex_ident_column primary_key_name=
    Lex_ident_column({STRING_WITH_LEN("PRIMARY")});

sql/sql_rename.cc

@@ -234,7 +234,7 @@ do_rename_temporary(THD *thd, TABLE_LIST *ren_table, TABLE_LIST *new_table)
 
 struct rename_param
 {
-  LEX_CSTRING old_alias, new_alias;
+  Lex_ident_table old_alias, new_alias;
   LEX_CUSTRING old_version;
   handlerton *from_table_hton;
 };
@@ -260,10 +260,10 @@ struct rename_param
 
 static int
 check_rename(THD *thd, rename_param *param,
-             TABLE_LIST *ren_table,
-             const LEX_CSTRING *new_db,
-             const LEX_CSTRING *new_table_name,
-             const LEX_CSTRING *new_table_alias,
+             const TABLE_LIST *ren_table,
+             const Lex_ident_db &new_db,
+             const Lex_ident_table &new_table_name,
+             const Lex_ident_table &new_table_alias,
              bool if_exists)
 {
   DBUG_ENTER("check_rename");
@@ -273,12 +273,12 @@ check_rename(THD *thd, rename_param *param,
   if (lower_case_table_names == 2)
   {
     param->old_alias= ren_table->alias;
-    param->new_alias= *new_table_alias;
+    param->new_alias= new_table_alias;
   }
   else
   {
     param->old_alias= ren_table->table_name;
-    param->new_alias= *new_table_name;
+    param->new_alias= new_table_name;
   }
   DBUG_ASSERT(param->new_alias.str);
 
@@ -304,7 +304,7 @@ check_rename(THD *thd, rename_param *param,
     DBUG_RETURN(-1);
   }
 
-  if (ha_table_exists(thd, new_db, &param->new_alias, NULL, NULL, 0))
+  if (ha_table_exists(thd, &new_db, &param->new_alias, NULL, NULL, 0))
   {
     my_error(ER_TABLE_EXISTS_ERROR, MYF(0), param->new_alias.str);
     DBUG_RETURN(1);                     // This can't be skipped
@@ -335,19 +335,18 @@ check_rename(THD *thd, rename_param *param,
 */
 
 static bool
-do_rename(THD *thd, rename_param *param, DDL_LOG_STATE *ddl_log_state,
-          TABLE_LIST *ren_table, const LEX_CSTRING *new_db,
+do_rename(THD *thd, const rename_param *param, DDL_LOG_STATE *ddl_log_state,
+          TABLE_LIST *ren_table, const Lex_ident_db *new_db,
           bool skip_error, bool *force_if_exists)
 {
   int rc= 1;
   handlerton *hton;
-  LEX_CSTRING *old_alias, *new_alias;
   TRIGGER_RENAME_PARAM rename_param;
   DBUG_ENTER("do_rename");
   DBUG_PRINT("enter", ("skip_error: %d", (int) skip_error));
 
-  old_alias= &param->old_alias;
-  new_alias= &param->new_alias;
+  const Lex_ident_table * const old_alias= &param->old_alias;
+  const Lex_ident_table * const new_alias= &param->new_alias;
   hton=      param->from_table_hton;
 
   DBUG_ASSERT(!thd->locked_tables_mode);
@@ -367,11 +366,11 @@ do_rename(THD *thd, rename_param *param, DDL_LOG_STATE *ddl_log_state,
 
     /* Check if we can rename triggers */
     if (Table_triggers_list::prepare_for_rename(thd, &rename_param,
-                                                &ren_table->db,
-                                                old_alias,
-                                                &ren_table->table_name,
-                                                new_db,
-                                                new_alias))
+                                                ren_table->db,
+                                                *old_alias,
+                                                ren_table->table_name,
+                                                *new_db,
+                                                *new_alias))
       DBUG_RETURN(!skip_error);
 
     thd->replication_flags= 0;
@@ -523,9 +522,9 @@ rename_tables(THD *thd, TABLE_LIST *table_list, DDL_LOG_STATE *ddl_log_state,
     {
       int error;
       rename_param param;
-      error= check_rename(thd, &param, ren_table, &new_table->db,
-                          &new_table->table_name,
-                          &new_table->alias, (skip_error || if_exists));
+      error= check_rename(thd, &param, ren_table, new_table->db,
+                          new_table->table_name,
+                          new_table->alias, (skip_error || if_exists));
       if (error < 0)
         continue;                               // Ignore rename (if exists)
       if (error > 0)