[FOLLOWUP][FEATURE] Allow EXT: syntax in PageRenderer and Compressor

The stylesheet files are included now by the PageRenderer to convert the
EXT: prefix into a real path, avoiding ERR_UNKNOWN_URL_SCHEME errors.

Resolves: #77589
Releases: master
Change-Id: I451604772f1e89957af73d68daf8a3d843b96731
Reviewed-on: https://review.typo3.org/49672


Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Bamboo TYPO3com <info@typo3.com>
Reviewed-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>