[TASK] Prepare TemplatePaths for new Fluid version

Some type hints in TYPO3's TemplatePaths implementation need to
be adjusted due to changes in the parent class. Also,
`ensureAbsolutePath()` now only handles `string` as input, as the
parent class is the only position the method is called and only strings
are valid in that context.

Resolves: #104783
Releases: main
Change-Id: I89fddd085a2a5fde11df769964eb9d129587b569
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/85830


Tested-by: Garvin Hicking <gh@faktor-e.de>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Simon Praetorius <simon@praetorius.me>
Reviewed-by: Simon Praetorius <simon@praetorius.me>
Reviewed-by: Garvin Hicking <gh@faktor-e.de>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Stefan Bürk <stefan@buerk.tech>