System environment check is not standalone
TYPO3\CMS\Install\SystemEnvironment\Check cannot be used without having a fully set up TYPO3 installation but claims that it should. All checks which require a fully set up TYPO3 should be separated and executed where necessary.
[BUGFIX] Make environment check standalone
The system environment check is supposed to be useable standalone
without any TYPO3 internal requirements.
Move all checks which require a fully set up TYPO3 installation
into a separate class and use it where necessary.
Reviewed-by: Benni Mack <email@example.com>
Tested-by: Benni Mack <firstname.lastname@example.org>
Reviewed-by: Andreas Wolf <email@example.com>
Tested-by: Andreas Wolf <firstname.lastname@example.org>