MDEV-20912 Add support for utf8mb4_0900_* collations in MariaDB Server

This is done by mapping most of the existing MySQL unicode 0900 collations
to MariadB 1400 unicode collations. The assumption is that 1400 is a super
set of 0900 for all practical purposes.

I also added a new function 'compare_collations()' and changed most code
to use this instead of comparing character sets directly.
This enables one to seamlessly mix-and-match the corresponding 0900 and
1400 sets. Field comparision and alter table treats the character sets
as identical.

All MySQL 8.0 0900 collations are supported except:
- utf8mb4_ja_0900_as_cs
- utf8mb4_ja_0900_as_cs_ks
- utf8mb4_ru_0900_as_cs
- utf8mb4_zh_0900_as_cs

These do not have corresponding entries in the MariadB 01400 collations.

Other things:
- Added COMMENT colum to information_schema.collations. For utf8mb4_0900
  colletions it contains the corresponding alias collation.

include/m_ctype.h

@@ -458,9 +458,9 @@ typedef struct my_charset_loader_st
 {
   char error[128];
   void *(*once_alloc)(size_t);
-  void *(*malloc)(size_t);
-  void *(*realloc)(void *, size_t);
-  void (*free)(void *);
+  void *(*malloc)(size_t);                      /* Not used */
+  void *(*realloc)(void *, size_t);             /* Not used */
+  void (*free)(void *);                         /* Not used */
   void (*reporter)(enum loglevel, const char *format, ...);
   int  (*add_collation)(struct charset_info_st *cs);
 } MY_CHARSET_LOADER;
@@ -1693,6 +1693,7 @@ 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 
 {

include/my_sys.h

@@ -1119,6 +1119,9 @@ static inline my_bool my_charset_same(CHARSET_INFO *cs1, CHARSET_INFO *cs2)
 extern my_bool init_compiled_charsets(myf flags);
 extern void add_compiled_collation(struct charset_info_st *cs);
 extern void add_compiled_extra_collation(struct charset_info_st *cs);
+extern my_bool add_alias_for_collation(LEX_CSTRING *collation_name,
+                                       LEX_CSTRING *alias,
+                                       uint alias_id);
 extern size_t escape_string_for_mysql(CHARSET_INFO *charset_info,
                                       char *to, size_t to_length,
                                       const char *from, size_t length,

mysql-test/main/ctype_ldml.result

@@ -456,43 +456,43 @@ select "foo" = "foo " collate latin1_test;
 1
 The following tests check that two-byte collation IDs work
 select * from information_schema.collations where id>256 and is_compiled<>'Yes' order by id;
-COLLATION_NAME	CHARACTER_SET_NAME	ID	IS_DEFAULT	IS_COMPILED	SORTLEN
-ascii2_general_nopad_ci	ascii2	318			1
-ascii2_bin2	ascii2	319			1
-ascii2_general_ci	ascii2	320	Yes		1
-ascii2_bin	ascii2	321			1
-ascii2_general_inherited_ci	ascii2	322			1
-ascii2_general_inherited2_ci	ascii2	323			1
-ascii2_badly_inherited_ci	ascii2	324			1
-ascii2_nopad_bin	ascii2	325			1
-utf8mb4_test_ci	utf8mb4	326			8
-utf16_test_ci	utf16	327			8
-utf8mb4_test_400_ci	utf8mb4	328			8
-utf8mb4_test_520_nopad_ci	utf8mb4	329			8
-utf8mb4_uca1400_test01_as_ci	utf8mb4	330			4
-latin1_test	latin1	331			1
-latin1_test2	latin1	332			1
-latin1_test2_cs	latin1	333			1
-latin1_swedish_nopad2_ci	latin1	334			1
-utf8mb3_bengali_standard_ci	utf8mb3	336			8
-utf8mb3_bengali_traditional_ci	utf8mb3	337			8
-utf8mb3_implicit_weights_ci	utf8mb3	338			8
-utf8mb3_phone_ci	utf8mb3	352			8
-utf8mb3_test_ci	utf8mb3	353			8
-utf8mb3_5624_1	utf8mb3	354			8
-utf8mb3_5624_2	utf8mb3	355			8
-utf8mb3_5624_3	utf8mb3	356			8
-utf8mb3_5624_4	utf8mb3	357			8
-ucs2_test_ci	ucs2	358			8
-ucs2_vn_ci	ucs2	359			8
-ucs2_5624_1	ucs2	360			8
-utf8mb3_5624_5	utf8mb3	368			8
-utf8mb3_5624_5_bad	utf8mb3	369			8
-utf8mb3_czech_test_w2	utf8mb3	370			4
-utf8mb3_czech_test_nopad_w2	utf8mb3	371			4
-utf8mb3_czech_test_bad_w2	utf8mb3	372			4
-utf32_test_ci	utf32	391			8
-utf8mb3_maxuserid_ci	utf8mb3	2047			8
+COLLATION_NAME	CHARACTER_SET_NAME	ID	IS_DEFAULT	IS_COMPILED	SORTLEN	COMMENT
+ascii2_general_nopad_ci	ascii2	318			1	
+ascii2_bin2	ascii2	319			1	
+ascii2_general_ci	ascii2	320	Yes		1	
+ascii2_bin	ascii2	321			1	
+ascii2_general_inherited_ci	ascii2	322			1	
+ascii2_general_inherited2_ci	ascii2	323			1	
+ascii2_badly_inherited_ci	ascii2	324			1	
+ascii2_nopad_bin	ascii2	325			1	
+utf8mb4_test_ci	utf8mb4	326			8	
+utf16_test_ci	utf16	327			8	
+utf8mb4_test_400_ci	utf8mb4	328			8	
+utf8mb4_test_520_nopad_ci	utf8mb4	329			8	
+utf8mb4_uca1400_test01_as_ci	utf8mb4	330			4	
+latin1_test	latin1	331			1	cp1252 West European
+latin1_test2	latin1	332			1	cp1252 West European
+latin1_test2_cs	latin1	333			1	cp1252 West European
+latin1_swedish_nopad2_ci	latin1	334			1	cp1252 West European
+utf8mb3_bengali_standard_ci	utf8mb3	336			8	
+utf8mb3_bengali_traditional_ci	utf8mb3	337			8	
+utf8mb3_implicit_weights_ci	utf8mb3	338			8	
+utf8mb3_phone_ci	utf8mb3	352			8	
+utf8mb3_test_ci	utf8mb3	353			8	
+utf8mb3_5624_1	utf8mb3	354			8	
+utf8mb3_5624_2	utf8mb3	355			8	
+utf8mb3_5624_3	utf8mb3	356			8	
+utf8mb3_5624_4	utf8mb3	357			8	
+ucs2_test_ci	ucs2	358			8	
+ucs2_vn_ci	ucs2	359			8	
+ucs2_5624_1	ucs2	360			8	
+utf8mb3_5624_5	utf8mb3	368			8	
+utf8mb3_5624_5_bad	utf8mb3	369			8	
+utf8mb3_czech_test_w2	utf8mb3	370			4	
+utf8mb3_czech_test_nopad_w2	utf8mb3	371			4	
+utf8mb3_czech_test_bad_w2	utf8mb3	372			4	
+utf32_test_ci	utf32	391			8	
+utf8mb3_maxuserid_ci	utf8mb3	2047			8	
 show collation like '%test%';
 Collation	Charset	Id	Default	Compiled	Sortlen
 latin1_test	latin1	331			1