[TASK] Refactor AssetCollector tests

In preparation for changes on `AssetRenderer`, most of the
unit tests are converted to functional tests. The test cases
are preserved, but duplicated to cover both the new
functional and the old unit tests.

Resolves: #104854
Releases: main
Change-Id: I3ab5bad81d7554061ca4d2ef61946e8282dc8f85
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/85921


Reviewed-by: Simon Praetorius <simon@praetorius.me>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Simon Schaufelberger <simonschaufi+typo3@gmail.com>
Tested-by: Simon Praetorius <simon@praetorius.me>