* 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
For ?, provide two code fixes, one for jsdoc/closure semantics
(`?t -> t | null)` and one for flow semantics
(`?t -> t | null | undefined`).
The current way of doing this is the hackiest thing you can imagine, but
it was easier than lifting everything into the list monad for a code fix
that I might not actually keep.