MDEV-31982 Remove check_db_name() from prepare_db_action()

- Adding a new class Lex_ident_db, to store normalized database names:
  lower-cased if lower-case-table-name says so,
  and checked to be a valid database name using Lex_ident_fs::check_db_name()

- Reusing the new class in parameters to functions:
    prepare_db_action()
    mysql_create_db()
    mysql_alter_db()
    mysql_rm_db()
    mysql_upgrade_db()

This change removed two old-style check_db_name() calls.

sql/sql_class.cc

@@ -6078,6 +6078,26 @@ void THD::get_definer(LEX_USER *definer, bool role)
 }
 
 
+bool THD::check_slave_ignored_db_with_error(const Lex_ident_db &db) const
+{
+#ifdef HAVE_REPLICATION
+  if (slave_thread)
+  {
+    Rpl_filter *rpl_filter;
+    rpl_filter= system_thread_info.rpl_sql_info->rpl_filter;
+    if (!rpl_filter->db_ok(db.str) ||
+        !rpl_filter->db_ok_with_wild_table(db.str))
+    {
+      my_message(ER_SLAVE_IGNORED_TABLE,
+                 ER_THD(this, ER_SLAVE_IGNORED_TABLE), MYF(0));
+      return true;
+    }
+  }
+#endif
+  return false;
+}
+
+
 /**
   Mark transaction to rollback and mark error as fatal to a sub-statement.