[TASK] EXT:form - use own folder for form definitions

Change default filemount for form definitions to fileadmin/form_definitions,
the directory is automatically created if necessary.

Existing forms in fileadmin/user_upload can be listed, duplicated and removed
but not edited.

Since no migration wizard can be provided for this, a manual migration is
necessary which can be done

1) ...by moving all form definitions to the new directory via filesystem or
2) ...by duplicating all form definitions (thus storing them in the new
location) and removing the old form definitions.

Resolves: #82328
Releases: master
Change-Id: Id804f58747a203e92998aca2699b37f81900e9e7
Reviewed-on: https://review.typo3.org/53989


Reviewed-by: Daniel Lorenz <daniel.lorenz@extco.de>
Tested-by: TYPO3com <no-reply@typo3.com>
Tested-by: Daniel Lorenz <daniel.lorenz@extco.de>
Reviewed-by: Mathias Brodala <mbrodala@pagemachine.de>
Tested-by: Mathias Brodala <mbrodala@pagemachine.de>
Reviewed-by: Carlos Meyer <cm@davitec.de>
Tested-by: Carlos Meyer <cm@davitec.de>
Reviewed-by: Bjoern Jacob <bjoern.jacob@tritum.de>
Tested-by: Bjoern Jacob <bjoern.jacob@tritum.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>