Following up from https://www.mediawiki.org/wiki/Topic:Udshhbynqffmjtc1 (which we need to decide if we're following normal deprecation policy, so in most cases, remove in the next MW major version if unused elsewhere) we should make sure all class_alias calls in MW core are tagged with at least @deprecated tags, and possibly a @since tag for its addition/renaming.
These should also be noted in RELEASE-NOTES
Makes later removal easier (when no longer used in extensions etc), without having to git blame each individually, as we know which MW Version it was renamed in.
Timestamp.php does this properly:
/** * @deprecated since 1.29 * @since 1.20 */ class_alias( Wikimedia\Timestamp\TimestampException::class, 'TimestampException' );