mysql_prepare_create_table() does my_qsort(sort_keys) on key
info. This sorting is indeterministic: a table is created with one
order and inplace alter may overwrite frm with another order. Since
inplace alter does nothing about key info for MyISAM/Aria storage
engines this results in discrepancy between frm and storage engine key
definitions.

The fix avoids the sorting of keys when no new keys added by ALTER
(and this is ok for MyISAM/Aria since it cannot add new keys inplace).

Notes:

mi_keydef_write()/mi_keyseg_write() are used only in mi_create(). They
should be used in ha_inplace_alter_table() as well.

Aria corruption detection is unimplemented: maria_check_definition()
is never used!

MySQL 8.0 has this bug as well as of 8.0.26.

This breaks main.long_unique in 10.4. The new result is correct and
should be applied as it just different (original) order of keys.