[BUGFIX] Use Context API for TemplateService->versionOL

The Context API can be used now within
TemplateService to fetch a version overlay, which now
only relies on the PageRepository (which also uses Context API),
to avoid certain magic detection of Frontend/Backend mode.

TemplateService is only used to fetch sys_template
records in this use-case.

Resolves: #88626
Releases: master
Change-Id: I5f6526868af090915748031d50eeaf245049e655
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/61126


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Daniel Gorges <daniel.gorges@b13.de>
Tested-by: Daniel Goerz <daniel.goerz@posteo.de>
Reviewed-by: Daniel Gorges <daniel.gorges@b13.de>
Reviewed-by: Daniel Goerz <daniel.goerz@posteo.de>