[TASK] Use ModuleTemplate in LoginController

ModuleTemplate has been introduced in TYPO3 v7 to
supersed DocumentTemplate. LoginController is one of
the few places in TYPO3 Backend where the old API is still
used.

The patch uses ModuleTemplate and avoids using Fluid view in Fluid view
by using ModuleTemplates' already established View.

Resolves: #90304
Releases: master
Change-Id: I2dbee8dd4a031a6ceabd74d6650b9b4cfc6893a6
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/63157


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>