MDEV-11777 REGEXP_REPLACE converts utf8mb4 supplementary characters to '?'

use utf8mb4 with PCRE2, not utf8mb3

mysql-test/main/func_regexp_pcre.result

@@ -895,3 +895,12 @@ REGEXP_INSTR('a_kollision', 'o([lm])\\1')
 REGEXP_INSTR('a_kollision', '(oll)')
 4
 SELECT REGEXP_INSTR('a_kollision', 'o([lm])\\1');
+REGEXP_INSTR('a_kollision', 'o([lm])\\1')
+4
+SELECT a FROM (SELECT "aa" a) t WHERE a REGEXP '[0-9]';
+a
+#
+# MDEV-11777 REGEXP_REPLACE converts utf8mb4 supplementary characters to '?'
+#
+select hex(regexp_replace(cast(x'F09F9881' as char character set 'utf8mb4'), _utf8mb4'a', _utf8mb4'b')) as Text;
+Text

mysql-test/main/func_regexp_pcre.test

@@ -470,3 +470,11 @@ SELECT REGEXP_INSTR('a_kollision', 'o([lm])\\1');
 #
 SELECT a FROM (SELECT "aa" a) t WHERE a REGEXP '[0-9]';
 --enable_service_connection
+
+--echo #
+--echo # MDEV-11777 REGEXP_REPLACE converts utf8mb4 supplementary characters to '?'
+--echo #
+select hex(regexp_replace(cast(x'F09F9881' as char character set 'utf8mb4'), _utf8mb4'a', _utf8mb4'b')) as Text;
+--echo #
+--echo # End of 10.6 tests
+--echo #

sql/item_cmpfunc.cc

@@ -6096,7 +6096,7 @@ void Regexp_processor_pcre::init(CHARSET_INFO *data_charset, int extra_flags)
 
   // Convert text data to utf-8.
   m_library_charset= data_charset == &my_charset_bin ?
-                     &my_charset_bin : &my_charset_utf8mb3_general_ci;
+                     &my_charset_bin : &my_charset_utf8mb4_general_ci;
 
   m_conversion_is_needed= (data_charset != &my_charset_bin) &&
                           !my_charset_same(data_charset, m_library_charset);

sql/item_cmpfunc.h

@@ -3057,7 +3057,7 @@ public:
     m_pcre(NULL), m_pcre_match_data(NULL),
     m_conversion_is_needed(true), m_is_const(0),
     m_library_flags(0),
-    m_library_charset(&my_charset_utf8mb3_general_ci)
+    m_library_charset(&my_charset_utf8mb4_general_ci)
   {}
   int default_regex_flags();
   void init(CHARSET_INFO *data_charset, int extra_flags);