[TASK] Migrate @typo3/form/backend/form-editor/mediator to TypeScript

Resolves: #101738
Related: #82577
Releases: main, 12.4
Change-Id: Id857430ae81322cf9197ba6df422780695f59f50
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/80630


Tested-by: core-ci <typo3@b13.com>
Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Benjamin Franzke <ben@bnf.dev>
Reviewed-by: Benjamin Kott <benjamin.kott@outlook.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Benjamin Kott <benjamin.kott@outlook.com>
Tested-by: Benjamin Franzke <ben@bnf.dev>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>