[TASK] Replace PATH_thisScript with Environment API call

All occurrences in the TYPO3 core have been replaced with
Environment::getCurrentScript() in order to slowly migrate
away from constants, and also detect dependencies to Environment
related functionality easier.

Resolves: #84883
Releases: master
Change-Id: I5197020bb539d9471cfa2aa3c7a09fa4b1a7d83c
Reviewed-on: https://review.typo3.org/56819


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Tymoteusz Motylewski <t.motylewski@gmail.com>
Tested-by: Tymoteusz Motylewski <t.motylewski@gmail.com>