[BUGFIX] Make JavaScript of SlugElement a real independent instance

The JavaScript for the SlugElement is partially designed to be a
independent instance for each slug field. However, this does not work for
mass editing the slug fields, as the `initialize()` method is always
called on the same instance.

This patch does multiple things:

- The JavaScript is converted to a TypeScript basis, which allows better
  handling of each instance
- The "Regenerate slug" button is disabled in case the "feeder" fields
  are not available to avoid getting bogus values

Resolves: #86221
Releases: master
Change-Id: I458247beb597c77407e94ce633314ae2e2d7095a
Reviewed-on: https://review.typo3.org/58273


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Frank Naegler <frank.naegler@typo3.org>
Tested-by: Frank Naegler <frank.naegler@typo3.org>