Mysql ddl compiler fall back to default index args

Mysql ddl compiler fall back to default index args

Fixed issue where DDL compilation options were registered to the hard-coded
dialect name ``mysql``. This made it awkward for MySQL-derived dialects
like MariaDB, StarRocks, etc. to work with such options when different sets
of options exist for different platforms. Options are now registered under
the actual dialect name, and a fallback was added to help avoid errors when
an option does not exist for that dialect. Pull request courtesy Tiansu Yu.

Fixes: #13134
Closes: #13138
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/13138
Pull-request-sha: 1bc953a2a1be97f82cdbbbc0d8961361716190fa

Change-Id: Ifa700a4e34da4d1923e9473dd8f0d2417dcfded4
(cherry picked from commit 8c262051247d5d83f3d0269003705a363dbc3e60)