[TASK] Migrate EXT:backend Login.js and UserPassLogin.js to TypeScript

Resolves: #82594
Resolves: #82608
Releases: master
Change-Id: Ibc3fce2983d5a193db17d8acc1c4dab2baee31db
Reviewed-on: https://review.typo3.org/54371


Reviewed-by: Andreas Fernandez <typo3@scripting-base.de>
Tested-by: Andreas Fernandez <typo3@scripting-base.de>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Andreas Wolf <andreas.wolf@typo3.org>
Tested-by: Andreas Wolf <andreas.wolf@typo3.org>