1. Retain surrounding trivia when swapping the keyword.
2. Insert commas at the full-starts, rather than starts, of existing
keywords when merging with existing implements clauses.
Fixes#18794
* Fix#19959 and #19958: Remove un-localizable messages
* Update message
* Reorder error messages
* Fix https://github.com/Microsoft/TypeScript/issues/15399: remove periods at the end of messages
* Accept baselines for error code changes
* accept baselines for removed periods
* Update diagnostic messages