Support RENAME column syntax from MySQL 8.0

There are new DDL constructs as of 8.0. E.g. it's now possible to rename a column without repeating its definition:

ALTER TABLE foo RENAME COLUMN old TO new;

We should check with the upstream grammar provided by Antlr, whether it has already been updated and if not look into collaborating with them. 8.0 support should only be provided for the new Antlr-based parser and not the legacy one.