[TASK] Allow Symfony 4 as constraint for composer

Symfony4 was released today, and using Symfony 4 components
should not be restricted.

The current used Symfony components (YAML, Finder, Console)
mainly concentrated on cleanup for the code.

For the bundled zip/tar.gz archives, nothing changes.

Resolves: #83180
Releases: master, 8.7
Change-Id: Ic518f3b7d3a94bd3b89587d4c8a07ed37c71cb38
Reviewed-on: https://review.typo3.org/54893


Reviewed-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Tested-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Susanne Moog <susanne.moog@typo3.org>
Tested-by: Susanne Moog <susanne.moog@typo3.org>