[TASK] Enforce TYPO3 Composer Installers package v5

Composer-based installations will now have their
extensions within composers' vendor folder
instead of typo3/sysext/ and typo3conf/ext/.

This way, all non-public files are moved outside
the document root (ideally), while public files
within extensions are symlinked to public/_assets/.

TYPO3 will then resolve "EXT:" syntax depending
on public / private folders to their respective
locations.

Used commands:
- composer req "typo3/cms-composer-installers:^5.0"
- composer req "typo3/cms-composer-installers:^5.0" --no-update -d typo3/sysext/core

Resolves: #98484
Releases: main
Change-Id: Ia790e9e306ec142a0c581b801936d6b2c36e5c46
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/75917


Tested-by: Benjamin Franzke <bfr@qbus.de>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Benjamin Franzke <bfr@qbus.de>
Reviewed-by: Oliver Hader <oliver.hader@typo3.org>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Benni Mack <benni@typo3.org>