[TASK] Remove then() callback hell in EXT:form wizard

The code of the form creation wizard is cleaned up a bit. The nested
`then()` callback hell is replaced with proper async/await statements to
make the code more readable.

Resolves: #103156
Releases: main
Change-Id: I144d6be0c3608f7d412dbefd031dd4d0ce4a3a42
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/83041
Tested-by: Benjamin Franzke <ben@bnf.dev>
Tested-by: Andreas Nedbal <andy@pixelde.su>
Reviewed-by: Benjamin Franzke <ben@bnf.dev>
Reviewed-by: Andreas Kienast <a.fernandez@scripting-base.de>
Reviewed-by: Andreas Nedbal <andy@pixelde.su>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Andreas Kienast <a.fernandez@scripting-base.de>