[BUGFIX] Label Userfunction shows wrong infos

Refactored userfunction for generating DCE field labels, to work correctly with sections and child fields inside of sections.

Resolves: #59920
Change-Id: Icf5c35fe66dc6ca9e23a31cb49ec73e45f4e407a
Reviewed-on: https://review.typo3.org/31167
Reviewed-by: Armin Ruediger Vieweg
Tested-by: Armin Ruediger Vieweg