[TASK] Tests: Find all tests automatically

All regular unit tests are located at
typo3/sysext/"extension"/Tests/Unit. The patch substitutes the single
suite registration in UnitTests.xml with a wildcard, only "Legacy"
and "Integration" tests are still registered as special locations.

Following this schema, tests located at default locations within
extensions will be found automatically without explicit registration.

Resolves: #58533
Related: #51436
Releases: 6.2
Change-Id: Ic822a68f60060437d2e3aabea7754f5b1e72af50
Reviewed-on: https://review.typo3.org/29879
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn