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_partition_admin.cc

@@ -507,7 +507,6 @@ bool Sql_cmd_alter_table_exchange_partition::
   TABLE_LIST *swap_table_list;
   handlerton *table_hton;
   partition_element *part_elem;
-  const char *partition_name;
   char temp_name[FN_REFLEN+1];
   char part_file_name[2*FN_REFLEN+1];
   char swap_file_name[FN_REFLEN+1];
@@ -629,10 +628,10 @@ bool Sql_cmd_alter_table_exchange_partition::
   ddl_log.new_table_id.length= MY_UUID_SIZE;
 
   /* set lock pruning on first table */
-  partition_name= alter_info->partition_names.head();
+  const Lex_cstring_strlen partition_name= alter_info->partition_names.head();
   if (unlikely(table_list->table->part_info->
-               set_named_partition_bitmap(partition_name,
-                                          strlen(partition_name))))
+               set_named_partition_bitmap(partition_name.str,
+                                          partition_name.length)))
     DBUG_RETURN(true);
 
   if (unlikely(lock_tables(thd, table_list, table_counter, 0)))
@@ -1023,7 +1022,7 @@ bool alter_partition_convert_in(ALTER_PARTITION_PARAM_TYPE *lpt)
   const char *path= lpt->table_list->table->s->path.str;
   TABLE_LIST *table_from= lpt->table_list->next_local;
 
-  const char *partition_name=
+  const Lex_ident_partition &partition_name=
     thd->lex->part_info->curr_part_elem->partition_name;
 
   if (create_partition_name(part_file_name, sizeof(part_file_name), path,