[TASK] Replace further usages with Environment API

Most of the occurrences have been replaced by using
Environment API.

On top, labels are now moved into "var/labels"
for existing composer-based installations, moving
XLF files out of the document root when the environment
is configured to allow files outside of the document
root.

For non-composer-based installations, labels are still
available under "typo3conf/l10n".

Resolves: #85560
Releases: master
Change-Id: Ib0a9e8e3dcd685109b9d922aee1970e68b265179
Reviewed-on: https://review.typo3.org/57600


Reviewed-by: Frank Naegler <frank.naegler@typo3.org>
Tested-by: Frank Naegler <frank.naegler@typo3.org>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Susanne Moog <susanne.moog@typo3.org>
Tested-by: Susanne Moog <susanne.moog@typo3.org>