[BUGFIX] EXT:form - show message if a form could not be saved

Notify the user if the form could not be saved.

Also remove the timeout of the error messages to ensure editors
have enough time to read and understand the message.

Resolves: #82255
Resolves: #82381
Releases: master, 8.7
Change-Id: I1377b7a85347107e7d03079b5a31179873a81e60
Reviewed-on: https://review.typo3.org/54126


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Daniel Lorenz <daniel.lorenz@extco.de>
Tested-by: Daniel Lorenz <daniel.lorenz@extco.de>
Reviewed-by: Bjoern Jacob <bjoern.jacob@tritum.de>
Tested-by: Bjoern Jacob <bjoern.jacob@tritum.de>
Reviewed-by: Susanne Moog <susanne.moog@typo3.org>
Tested-by: Susanne Moog <susanne.moog@typo3.org>