MDEV-23408 Wrong result upon query from I_S and further Assertion `!alias_arg || strlen(alias_arg->str) == alias_arg->length' failed with certain connection charset

There were two independent problems which lead to the crash
and to the non-relevant records returned in I_S queries:

- The code in the I_S implementation was not secure
  about values with 0x00 bytes.
  It's fixed by using check_db_name() and check_table_name()
  inside make_table_name_list(), and by adding the test for
  0x00 inside check_table_name().

- The code in Item_string::print() did not convert
  strings without introducers when restoring
  the CREATE VIEW statement from an Item tree.
  This made wrong literals inside the "query" line in the view FRM file
  in cases when the VIEW parse time
  character_set_client!=character_set_connection.
  That's fixed by adding a proper conversion.

  This change also fixed a similar problem in SHOW PROCEDURE CODE -
  the literals were displayed in wrong character set in SP instructions
  in cases when the SP parse time
  character_set_client!=character_set_connection.

sql/sql_show.cc

@@ -4227,7 +4227,9 @@ make_table_name_list(THD *thd, Dynamic_array<LEX_STRING*> *table_names,
   if (!lookup_field_vals->wild_table_value &&
       lookup_field_vals->table_value.str)
   {
-    if (lookup_field_vals->table_value.length > NAME_LEN)
+    if (check_table_name(lookup_field_vals->table_value.str,
+                         lookup_field_vals->table_value.length,
+                         false))
     {
       /*
         Impossible value for a table name,
@@ -4264,6 +4266,9 @@ make_table_name_list(THD *thd, Dynamic_array<LEX_STRING*> *table_names,
     return (schema_tables_add(thd, table_names,
                               lookup_field_vals->table_value.str));
 
+  if (check_db_name((LEX_STRING*)db_name))
+    return 0; // Impossible TABLE_SCHEMA name
+
   find_files_result res= find_files(thd, table_names, db_name, path,
                                     &lookup_field_vals->table_value);
   if (res != FIND_FILES_OK)