MDEV-36213 Doubled memory usage (11.4.4 <-> 11.4.5)

Fixing the code adding MySQL _0900_ collations as _uca1400_ aliases
not to perform deep initialization of the corresponding _uca1400_
collations.

Only basic initialization is now performed which allows to watch
these collations (both _0900_ and _uca1400_) in queries to
INFORMATION_SCHEMA tables COLLATIONS and
COLLATION_CHARACTER_SET_APPLICABILITY,
as well as in SHOW COLLATION statements.

Deep initialization is now performed only when a collation
(either the _0900_ alias or the corresponding  _uca1400_ collation)
is used for the very first time after the server startup.

Refactoring was done to maintain the code easier:
- most of the _uca1400_ code was moved from ctype-uca.c
  to a new file ctype-uca1400.c
- most of the _0900_ code was moved from type-uca.c
  to a new file ctype-uca0900.c

Change details:

- The original function add_alias_for_collation() added by the patch for
   "MDEV-20912 Add support for utf8mb4_0900_* collations in MariaDB Server"
  was removed from mysys/charset.c, as it had two two problems:

  a. it forced deep initialization of the _uca1400_ collations
     when adding _0900_ aliases for them at the server startup
     (the main reported problem)

  b. the collation initialization code in add_alias_for_collation()
     was related more to collations rather than to memory management,
     so /strings should be a better place for it than /mysys.

  The code from add_alias_for_collation() was split into separate functions.
  Cyclic dependency was removed. `#include <my_sys.h>` was removed
  from /strings/ctype-uca.c. Collations are now added using a callback
  function MY_CHARSET_LOADED::add_collation, like it is done for
  user collations defined in Index.xml. The code in /mysys sets
  MY_CHARSET_LOADED::add_collation to add_compiled_collation().

- The function compare_collations() was removed.
  A new virtual function was added into my_collation_handler_st instead:

    my_bool (*eq_collation)(CHARSET_INFO *self, CHARSET_INFO *other);

  because it is the collation handler who knows how to detect equal
  collations by comparing only some of CHARSET_INFO members without
  their deep initialization.

  Three implementations were added:
  - my_ci_eq_collation_uca() for UCA collations, it compares
    _0900_ collations as equal to their corresponding _uca1400_ collations.
  - my_ci_eq_collation_utf8mb4_bin(), it compares
    utf8mb4_nopad_bin and utf8mb4_0900_bin as equal.
  - my_ci_eq_collation_generic() - the default implementation,
    which compares all collations as not equal.

  A C++ wrapper CHARSET_INFO::eq_collations() was added.
  The code in /sql was changes to use the wrapper instead of
  the former calls for the removed function compare_collations().

- A part of add_alias_for_collation() was moved into a new function
  my_ci_alloc(). It allocates a memory for a new charset_info_st
  instance together with the collation name and the comment using a single
  MY_CHARSET_LOADER::once_alloc call, which points to my_once_alloc()
  in the server.

- A part of add_alias_for_collation() was moved into a new function
  my_ci_make_comment_for_alias(). It makes an "Alias for xxx" string,
  e.g. "Alias for utf8mb4_uca1400_swedish_ai_ci" in case of
  utf8mb4_sv_0900_ai_ci.

- A part of the code in create_tailoring() was moved to
  a new function my_uca1400_collation_get_initialized_shared_uca(),
  to reuse the code between _uca1400_ and _0900_ collations.

- A new function my_collation_id_is_mysql_uca0900() was added
  in addition to my_collation_id_is_mysql_uca1400().

- Functions to build collation names were added:
   my_uca0900_collation_build_name()
   my_uca1400_collation_build_name()

- A shared function function was added:

  my_bool
  my_uca1400_collation_alloc_and_init(MY_CHARSET_LOADER *loader,
                                      LEX_CSTRING name,
                                      LEX_CSTRING comment,
                                      const uca_collation_def_param_t *param,
                                      uint id)

  It's reused to add _uca1400_ and _0900_ collations, with basic
  initialization (without deep initialization).

- The function add_compiled_collation() changed its return type from
  void to int, to make it compatible with MY_CHARSET_LOADER::add_collation.

- Functions mysql_uca0900_collation_definition_add(),
  mysql_uca0900_utf8mb4_collation_definitions_add(),
  mysql_utf8mb4_0900_bin_add() were added into ctype-uca0900.c.
  They get MY_CHARSET_LOADER as a parameter.

- Functions my_uca1400_collation_definition_add(),
  my_uca1400_collation_definitions_add() were moved from
  charset-def.c to strings/ctype-uca1400.c.
  The latter now accepts MY_CHARSET_LOADER as the first parameter
  instead of initializing a MY_CHARSET_LOADER inside.

- init_compiled_charsets() now initializes a MY_CHARSET_LOADER
  variable and passes it to all functions adding collations:
  - mysql_utf8mb4_0900_collation_definitions_add()
  - mysql_uca0900_utf8mb4_collation_definitions_add()
  - mysql_utf8mb4_0900_bin_add()

- A new structure was added into ctype-uca.h:

  typedef struct uca_collation_def_param
  {
    my_cs_encoding_t cs_id;
    uint tailoring_id;
    uint nopad_flags;
    uint level_flags;
  } uca_collation_def_param_t;

  It simplifies reusing the code for _uca1400_ and _0900_ collations.

- The definition of MY_UCA1400_COLLATION_DEFINITION was
  moved from ctype-uca.c to ctype-uca1400.h, to reuse
  the code for _uca1400_ and _0900_ collations.

- The definitions of "MY_UCA_INFO my_uca_v1400" and
  "MY_UCA_INFO my_uca1400_info_tailored[][]" were moved from
  ctype-uca.c to ctype-uca1400.c.

- The definitions/declarations of:
  - mysql_0900_collation_start,
  - struct mysql_0900_to_mariadb_1400_mapping
  - mysql_0900_to_mariadb_1400_mapping
  - mysql_utf8mb4_0900_collation_definitions_add()
  were moved from ctype-uca.c to ctype-uca0900.c

- Functions
  my_uca1400_make_builtin_collation_id()
  my_uca1400_collation_definition_init()
  my_uca1400_collation_id_uca400_compat()
  my_ci_get_collation_name_uca1400_context()
  were moved from ctype-uca.c to ctype-uca1400.c and ctype-uca1400.h

- A part of my_uca1400_collation_definition_init()
  was moved into my_uca0520_builtin_collation_by_id(),
  to make functions smaller.

include/m_ctype.h

@@ -568,6 +568,22 @@ struct my_collation_handler_st
   uint (*get_id)(CHARSET_INFO *cs, my_collation_id_type_t type);
   LEX_CSTRING (*get_collation_name)(CHARSET_INFO *cs,
                                     my_collation_name_mode_t mode);
+  /*
+    Check if two collations are equally defined, so DTCollation aggregation
+    code considers them as equal. This is useful for collation aliases,
+    e.g. for MySQL 0900 collation aliases for 1400 MariaDB collations.
+    For example, these queries work without raising "Illegal mix of collations":
+
+      SELECT _utf8mb4'a' COLLATE utf8mb4_uca1400_nopad_ai_ci =
+             _utf8mb4'a' COLLATE utf8mb4_0900_ai_ci;
+
+      SELECT ... WHERE column_with_collation_utf8mb4_uca1400_nopad_ai_ci =
+                       column_with_collation_tf8mb4_0900_ai_ci;
+
+    @return 0  Different
+    @return 1  Identical
+  */
+  my_bool (*eq_collation)(CHARSET_INFO *self, CHARSET_INFO *other);
 };
 
 
@@ -1110,6 +1126,19 @@ struct charset_info_st
   {
     return (coll->get_collation_name)(this, mode);
   }
+
+  /*
+    Check if two collations are equally defined. For details
+    see the definition of eq_collation() in my_collation_handler_st.
+
+    @return 0  Different
+    @return 1  Identical
+  */
+  my_bool eq_collation(CHARSET_INFO *rhs) const
+  {
+    return this == rhs || (coll->eq_collation)(this, rhs);
+  }
+
 #endif /* __cplusplus */
 };
 
@@ -1693,7 +1722,6 @@ my_bool my_propagate_complex(CHARSET_INFO *cs, const uchar *str, size_t len);
 uint my_ci_get_id_generic(CHARSET_INFO *cs, my_collation_id_type_t type);
 LEX_CSTRING my_ci_get_collation_name_generic(CHARSET_INFO *cs,
                                              my_collation_name_mode_t mode);
-my_bool compare_collations(CHARSET_INFO *cs1, CHARSET_INFO *cs2);
 
 typedef struct 
 {