[TASK] Disable scheduler-tests if EXT:scheduler not loaded

Change-Id: I62ec38fc27330e74c4bc3eed6ded3a2f4a6de550
Resolves: #51115
Releases: 6.2, 6.1, 6.0
Reviewed-on: https://review.typo3.org/23133
Reviewed-by: Anja Leichsenring
Tested-by: Anja Leichsenring
[TASK] Standalone functional test runner

Introduce base code for a standalone php test runner.

"./typo3conf/ext/phpunit/Composer/vendor/bin/phpunit
	-c typo3/sysext/core/Build/FunctionalTests.xml"

This way phpunit is called fully standalone and does not
depend on TYPO3 CMS bootstrap itself.

Resolves: #51111
Releases: 6.2
Change-Id: Ie790eec315f7a273fc62856df3169aa56b2ad60d
Reviewed-on: https://review.typo3.org/23131
Reviewed-by: Anja Leichsenring
Tested-by: Anja Leichsenring
Reviewed-by: Stefan Neufeind
Tested-by: Stefan Neufeind