[TASK] Use Environment API instead of PATH_site in t3editor

Resolves: #85275
Releases: master
Change-Id: Ib0a5a773387252609f01c07a441bdb183f5142c0
Reviewed-on: https://review.typo3.org/57232


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Jan Helke <typo3@helke.de>
Tested-by: Jan Helke <typo3@helke.de>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>