The form extension now features imports in YAML configuration files via
the special toplevel "imports" option. With the help of this feature,
form setup and especially form definitions can be reused without copying.

Furthermore, the YAML loading has been centralized and slightly extended
to meet the requirements of the form framework.

The configuration of the form framework has been merged into one file. A
follow up patch will rearrange the configuration to improve clarity and
understandability. This task heavily depends on the "imports"
functionality.

Resolves: #82089
Releases: master
Change-Id: I44f52572ab2d516949dd017ef1face351b448d65
Reviewed-on: https://review.typo3.org/54210


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Mathias Brodala <mbrodala@pagemachine.de>
Tested-by: Mathias Brodala <mbrodala@pagemachine.de>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Jigal van Hemert <jigal.van.hemert@typo3.org>
Tested-by: Jigal van Hemert <jigal.van.hemert@typo3.org>