[DBAL-1062] Fix renaming indexes used by foreign key constraints

Platforms that do not support a SQL syntax for natively renaming indexes need to drop and recreate indexes to perform a rename.
Platforms like MySQL < 5.7 deny dropping indexes used by foreign key constraints. In this case foreign key constraints have to be dropped before dropping indexes and have to be recreated after the particular index(es) have been recreated.
This is a major issue right now for people trying to upgrade to DBAL 2.5.
Can this new block be moved to a new private method? `getForeignKeyConstraintChangesSql()` maybe?