[TASK] Have LICENSE.txt in all core exts

Preparing the git split for better composer integration
we end up with single repos for all extensions and single
packagist packages.
All extensions thus need a specific LICENSE.txt now.

Change-Id: Ia77ae3e413e479ec7fa9438cbfc2abf808738111
Resolves: #81730
Releases: master, 8.7
Reviewed-on: https://review.typo3.org/53345


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>