[TASK] Simplify ext:fluid TemplatePaths

Inline some methods into getContextSpecificViewConfiguration()
and adapt tests. Note the calling fillDefaultsByPackageName()
will see a deprecation soon, this change is a preparation to
make that patch better readable.

Resolves: #104761
Releases: main
Change-Id: Ibb2bacb2de4fc98488701ada0480220c8d394041
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/85807


Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Simon Praetorius <simon@praetorius.me>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Simon Praetorius <simon@praetorius.me>