[TASK] Make use of autoloading for fixtures in testclasses

Autoloader can be used in almost all cases.

Change-Id: I853e85758f6b39a6cb0798891ca0bea40ad6915c
Resolves: #52357
Releases: 6.2
Reviewed-on: https://review.typo3.org/24131
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn