[FEATURE] Add methods to get class tag values via reflection

This patch adds ReflectionService::getClassTagsValues($className) and
ReflectionService::getClassTagValues($className, $tag) to get class
tag values via reflection.

Also the unit test changed to test the new methods.

Resolves: #60822
Releases: master
Change-Id: I45962c30f2559ad1b10fe33a64c541425c80db90
Reviewed-on: http://review.typo3.org/32714
Reviewed-by: Alexander Opitz <opitz.alexander@googlemail.com>
Tested-by: Alexander Opitz <opitz.alexander@googlemail.com>
Reviewed-by: Markus Klein <klein.t3@reelworx.at>
Tested-by: Markus Klein <klein.t3@reelworx.at>