[BUGFIX] Use temporary directory for exporting files

When adding exports into fileadmin, the files
are stored in a temporary folder, which is located
in typo3temp/var/transient/ - this folder does not
need to be accessed via FAL, as it also adds
some issues when this file is not inside the
document root, for this reason, the code is adapted
to work with the native File System directly, and
when moving to fileadmin/user_upload/_temp_/impexp/
then FAL is used again.

Resolves: #88815
Releases: master, 9.5
Change-Id: I633a5dbda595bef73b7420ad511e03c0f7054972
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/61336


Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Susanne Moog <look@susi.dev>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Susanne Moog <look@susi.dev>