Backporting a part of MDEV-32026 (which also fixed MDEV-32025 in 11.3)
from 11.3 to 10.4.

The reported crash happened with --lower-case-table-names=2
on statements like:

ALTER DATABASE Db1 DEFAULT CHARACTER SET utf8;
ALTER DATABASE `#mysql50#D+b1` UPGRADE DATA DIRECTORY NAME;

lock_schema_name() expects a normalized database name
and assert if a non-normalized name comes.

mysql_alter_db_internal() and mysql_upgrade_db() get
a non-normalized database name in the parameter.
Fixing them to normalize the database name before passing
it to lock_schema_name().