[TASK] Implement standalone functional test API

Test encapsulation and a controlled environment is
crucial for solid functional tests.

The patch creates a full TYPO3 CMS instance within
typo3temp/ together with an own database and
LocalConfiguration to run a specific functional test
in this environment. A full TYPO3 CMS bootstrap of
this instance is done. A new environment with a fresh
PHP process is created for each and every single test.

Functional test can use the API by calling parent::setUp()
and parent::tearDown().

The functional suite can be called directly with phpunit
"./typo3conf/ext/phpunit/Composer/vendor/bin/phpunit
	-c typo3/sysext/core/Build/FunctionalTests.xml"

Currently the test suite must be called from the document
root folder.

The patch is currently a base patch for the main API implementing
immediatly needed stuff. With further patches sanitizing and
more details will be added.

Change-Id: I54f652f6a346a5155b5c33e4a065ab37898ff5b2
Resolves: #51091
Releases: 6.2
Reviewed-on: https://review.typo3.org/23117
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn
Reviewed-by: Stefan Neufeind
Reviewed-by: Tymoteusz Motylewski
Tested-by: Tymoteusz Motylewski
Reviewed-by: Anja Leichsenring
Tested-by: Anja Leichsenring