[FEATURE] Add possibility to provide additional localization files

The AdditionalResourceService of the workspace module in the
backend currently allows to define custom JavaScript and
stylesheet resources. However, adding custom localization
files is missing and topic of this change.

Resolves: #65698
Releases: master
Change-Id: Ic9a3f004408b2406ac0e08fa2c96550cf059e3e8
Reviewed-on: http://review.typo3.org/37789


Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Benjamin Mack <benni@typo3.org>
Tested-by: Benjamin Mack <benni@typo3.org>