MDEV-14293: MyRocks lacks basic functionality

Adjust the fix according to the review input: don't introduce a special
error caode, use ER_INTERNAL_ERROR catch-all.

sql/share/errmsg-utf8.txt

@@ -7752,7 +7752,3 @@ ER_GEOJSON_EMPTY_COORDINATES
 
 ER_MYROCKS_CANT_NOPAD_COLLATION
   eng "MyRocks doesn't currently support collations with \"No pad\" attribute."
-
-ER_MYROCKS_COLLATION_IS_LIMITED
-  eng "Indexed column %s.%s uses a collation that does not allow index-only access in secondary key and has reduced disk space efficiency in primary key."
-

storage/rocksdb/ha_rocksdb.cc

@@ -6121,9 +6121,15 @@ int ha_rocksdb::create_cfs(
                 table_arg->key_info[i].key_part[part].field) &&
             !rdb_collation_exceptions->matches(tablename_sys)) {
 
-          my_error(ER_MYROCKS_COLLATION_IS_LIMITED, MYF(ME_JUST_WARNING),
-                   tbl_def_arg->full_tablename().c_str(),
-                   table_arg->key_info[i].key_part[part].field->field_name);
+          char buf[1024];
+          my_snprintf(buf, sizeof(buf),
+                      "Indexed column %s.%s uses a collation that does not "
+                      "allow index-only access in secondary key and has "
+                      "reduced disk space efficiency in primary key.",
+                       tbl_def_arg->full_tablename().c_str(),
+                       table_arg->key_info[i].key_part[part].field->field_name);
+
+          my_error(ER_INTERNAL_ERROR, MYF(ME_JUST_WARNING), buf);
         }
       }
     }

storage/rocksdb/mysql-test/rocksdb/r/add_index_inplace.result

@@ -287,7 +287,7 @@ CREATE TABLE t1 (a INT, b TEXT collate utf8_general_ci);
 # MariaDB no longer gives ER_UNSUPPORTED_COLLATION
 ALTER TABLE t1 ADD KEY kb(b(10));
 Warnings:
-Warning	4078	Indexed column test.t1.b uses a collation that does not allow index-only access in secondary key and has reduced disk space efficiency in primary key.
+Warning	1815	Internal error: Indexed column test.t1.b uses a collation that does not allow index-only access in secondary key and has reduced disk space efficiency in primary key.
 ALTER TABLE t1 ADD PRIMARY KEY(a);
 DROP TABLE t1;
 set global rocksdb_strict_collation_check= @tmp_rocksdb_strict_collation_check;