[BUGFIX] Prevent YAML escaping from being displayed in form labels

To make the form manager and form plugins load faster,
the patch https://review.typo3.org/c/Packages/TYPO3.CMS/+/58054/
optimized the parsing of form definitions. Instead of using the
YAML parser, a very rudimentary "parser" was introduced. This works
fine, except for the fact that YAML escapes in form labels
are not unescaped when displayed.

This patch partially reintroduces the parsing of YAML, but only for
the label.

The performance drops only slightly.

10000x "loadMetaData()" (status quo) = 0.41 seconds
10000x "loadMetaData()" + parse label with yaml parser = 0.57 seconds
10000x parse the whole form definition with yaml parser = 7.57 seconds

Resolves: #95733
Releases: main, 11.5
Change-Id: I742b18313af4c8fe90d2899848518d90f543f86e
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/73712


Tested-by: core-ci <typo3@b13.com>
Tested-by: Oliver Hader <oliver.hader@typo3.org>
Reviewed-by: Oliver Hader <oliver.hader@typo3.org>