[BUGFIX] Wait for document being ready before booting form editor

In some scenarios, it may happen that the DOM isn't ready while the
form editor is already booted, leading to JavaScript errors as DOM
nodes are not available yet.

The `dispatch*` methods in EXT:form's helper now wait for a ready state
before booting the form editor.

Resolves: #100651
Releases: main
Change-Id: Ic3f331d58fd9ae74e1d7dc121b6ae51c89c89cfc
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/78716


Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Benni Mack <benni@typo3.org>