[TASK] Have site attribute in filelist module

When the Site construct has been added to TYPO3
in v9, the setup together with PseudoSites was
pretty complex. This has been simplified meanwhile
and the resolved site is usually added to the
backend request as attribute.

Except in cases where GET / POST param "id" is
misused. This is the case in filelist module.

The patch changes the backend related SiteResolver
middleware to *always* add a site attribute to
the request, backend controllers can now rely
on it to be set, even if its just a NullSite.

Resolves: #99121
Related: #86153
Releases: main
Change-Id: I63ea9ed1b5bca5db298f7a3bf000fcb4f777f627
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/76665


Tested-by: core-ci <typo3@b13.com>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Christian Kuhn <lolli@schwarzbu...>