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")});

storage/perfschema/pfs_variable.cc

@@ -170,12 +170,12 @@ int PFS_system_variable_cache::do_materialize_global(void)
   for (SHOW_VAR *show_var= m_show_var_array.front();
        show_var->value && (show_var != m_show_var_array.end()); show_var++)
   {
-    const char* name= show_var->name;
+    const Lex_ident_sys_var name= Lex_cstring_strlen(show_var->name);
     sys_var *value= (sys_var *)show_var->value;
     assert(value);
 
     if ((m_query_scope == OPT_GLOBAL) &&
-        (!my_strcasecmp(system_charset_info, name, "sql_log_bin")))
+        name.streq("sql_log_bin"_LEX_CSTRING))
     {
       /*
         PLEASE READ:
@@ -665,9 +665,9 @@ bool PFS_status_variable_cache::filter_by_name(const SHOW_VAR *show_var)
   if (show_var->type == SHOW_ARRAY)
   {
     /* The SHOW_ARRAY name is the prefix for the variables in the subarray. */
-    const char *prefix= show_var->name;
+    const Lex_ident_sys_var prefix= Lex_cstring_strlen(show_var->name);
     /* Exclude COM counters if not a SHOW STATUS command. */
-    if (!my_strcasecmp(system_charset_info, prefix, "Com") && !m_show_command)
+    if (prefix.streq("Com"_LEX_CSTRING) && !m_show_command)
       return true;
   }
   else
@@ -679,12 +679,12 @@ bool PFS_status_variable_cache::filter_by_name(const SHOW_VAR *show_var)
       Assume null prefix to ensure that only server-defined slave status
       variables are filtered.
     */
-    const char *name= show_var->name;
-    if (!my_strcasecmp(system_charset_info, name, "Slave_running") ||
-        !my_strcasecmp(system_charset_info, name, "Slave_retried_transactions") ||
-        !my_strcasecmp(system_charset_info, name, "Slave_last_heartbeat") ||
-        !my_strcasecmp(system_charset_info, name, "Slave_received_heartbeats") ||
-        !my_strcasecmp(system_charset_info, name, "Slave_heartbeat_period"))
+    const Lex_ident_sys_var name= Lex_cstring_strlen(show_var->name);
+    if (name.streq("Slave_running"_LEX_CSTRING) ||
+        name.streq("Slave_retried_transactions"_LEX_CSTRING) ||
+        name.streq("Slave_last_heartbeat"_LEX_CSTRING) ||
+        name.streq("Slave_received_heartbeats"_LEX_CSTRING) ||
+        name.streq("Slave_heartbeat_period"_LEX_CSTRING))
     {
       return true;
     }