[BUGFIX] Only access FAL security checks when in Backend

The FAL security checks which adds additional checks for Backend Users
are currently placed within TYPO3_MODE === BE which applies to CLI as well.

In order to even use the FAL API via CLI, a user has to be authenticated (just for
browsing files). Therefore, the check needs to be handled via TYPO3_REQUEST_TYPE
which excludes symfony commands on CLI basis.

Additionally, the REQUEST TYPE checks are handled within the Slot and not
when to register the hook (see other cleanup patch as well).

Resolves: #82691
Releases: master, 8.7
Change-Id: I7b895a119a17ea166331eb1dbcb75e57fffbd388
Reviewed-on: https://review.typo3.org/54315


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Frans Saris <franssaris@gmail.com>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Andreas Fernandez <typo3@scripting-base.de>
Reviewed-by: Joerg Boesche <typo3@joergboesche.de>
Reviewed-by: Susanne Moog <susanne.moog@typo3.org>
Tested-by: Susanne Moog <susann...