[TASK] Modernize RootlineUtility tests

This is a late backport of a v13 patch to
prepare changes that have to go into v12
as bug fixes.

Tests:
* Merge remaining unit tests into functional tests.
* Switch from YAML based DB scenario creation to
  direct CSV import to gain more control in tests.
* Test reference index integrity of import CSV.
* Move some not related fixtures to a more suitable
  directory.

Resolves: #103566
Releases: main, 12.4
Change-Id: Ife5c2e115abfcf3f399ebc49dcf5759461812293
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/83731


Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>