[TASK] Move TSFE Initialization into a PSR-15 middleware

In order to have the main request handler only deal with content creation,
and especially to move fe_user / be_user initialization out of the RequestHandler,
and to remove dependencies from Bootstrap of the RequestHandler,
TSFE is now instantiated in a PSR-15 compatible middleware.

Resolves: #83928
Releases: master
Change-Id: I8a4dd4c10f5ea2eeb60f9870c34d04979a330826
Reviewed-on: https://review.typo3.org/55742


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Mathias Schreiber <mathias.schreiber@typo3.com>
Tested-by: Mathias Schreiber <mathias.schreiber@typo3.com>
Reviewed-by: Susanne Moog <susanne.moog@typo3.org>
Tested-by: Susanne Moog <susanne.moog@typo3.org>