[BUGFIX] Fix path-resolution for template-resource in EXT:felogin

Do not use frontend inclusion API for private template resource.
Instead resolve to full absolute path for inclusion.

Releases: master, 8.7
Resolves: #82978
Resolves: #82979
Change-Id: Iadd3a8386b967aeb8b5ffdb28baeb73c2a0f2734
Reviewed-on: https://review.typo3.org/54622


Reviewed-by: Andreas Fernandez <typo3@scripting-base.de>
Tested-by: Andreas Fernandez <typo3@scripting-base.de>
Reviewed-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Tested-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>