[TASK] Merge phpunit setup files to Build/phpunit

typo3/testing-framework ships default .xml and
bootstrap files for phpunit unit and functional tests.

They are however quite hard to maintain since the
testing-framework supports multiple core versions at
once, but core occassionally needs version specific
settings.

The patch copies the files from the testing-framework
to Build/phpunit and adapts core usages.

The files within testing-framework will be kept, but
will receive an additional "these are boilerplates,
consider copying them to your extension" hint for
extension developers.

The local .xml files are now:
* Compatible with phpunit 9
* Let tests fail if phpunit marks a test with warning.
  With this enabled, we would have seen the issues
  fixed with #94724 and #94723 with initial #94706
  already. Good to do that now.

Resolves: #94725
Related: #94706
Related: #94723
Related: #94724
Releases: master
Change-Id: I9fef75a972759d26d4e0e3286142cacf181c33d2
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/70239


Tested-by: core-ci <typo3@b13.com>
Tested-by: Benni Mack <benni@typo3.org>
Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>