[BUGFIX] Fix form manager new form creation wizard

The .done() Promise polyfill has been removed in #96263,
therefore .then() needs to be used on promised.

Also adapt the return type declaration
in the global type declarations file.

Resolves: #96328
Related: #96263
Releases: main
Change-Id: Iba53393076285db1709ac3980eeb434862ee2952
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/72618


Tested-by: core-ci <typo3@b13.com>
Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: Benni Mack <benni@typo3.org>
Tested-by: Benjamin Franzke <bfr@qbus.de>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Benjamin Franzke <bfr@qbus.de>