[FEATURE] Introduce AssetRenderer BeforeRendering events

AssetRenderer gets events for manipulating AssetCollector assets.

This enables asset post-processing extensions like EXT:min or
EXT:ws_scss to fully support AssetCollector assets.

The AssetCollector::add*() methods get an optional parameter that
allows filtering for (non-)priority assets. It became apararent during
testing that any listener would otherwise have to implement that
itself in order to avoid double-processing assets (as there are two
rendering passes, priority and non-priority).

Resolves: #90899
Releases: master
Change-Id: I2526328d3ee4ab269fa654347abd6156ee516a84
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/64021


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Benni Mack <benni@typo3.org>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>