[TASK] Use `requestSubmit()` in FormEngine

FormEngine JavaScript now uses `requestSubmit()` to announce an actual
data-changing submit action which allows binding to the `submit` event.
Also, this allows some refactorings in the future.

In the past, an artifical `dispatchSubmitEvent()` method was used to
achieve the same, that is now removed.

Resolves: #101794
Releases: main
Change-Id: I60fcd19f946ff91da736ec2c74fdf41365429cee
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/80754


Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Stefan B�rk <stefan@buerk.tech>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Stefan B�rk <stefan@buerk.tech>
Tested-by: core-ci <typo3@b13.com>