[!!!][TASK] Remove TSFE->no_cacheBeforePageGen "safety net"

TypoScriptFrontendController->no_cacheBeforePageGen is a flag
used by generatePage_preProcessing() to ensure an extension
never sets no_cache=false when it has been set to true before
since this would lead to broken cache handling: FE Caching
must never be enabled again after it has been disabled once.

Upcoming patches model the cache information differently and
will no longer allow re-enabling caching when it has been
enabled once - at least if an extension does not do very
hacky request manipulations.

The patch removes this "safety net" since it collides with
upcoming changes.

Method and property are internal handling, but the method
has unfortunately never been set @internal, which is why
this patch is marked as breaking.

Resolves: #102590
Releases: main
Change-Id: If4abc1333c81b6bdfd361a053c67674004879ef5
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/82074


Tested-by: core-ci <typo3@b13.com>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>