[TASK] Migrate SelectElementTree to TypeScript

This patch migrates FormEngine's SelectElementTree to TypeScript.
Also, a terrible hack that puts the local tree initialitation callback
into global scope has been removed.

Resolves: #87987
Releases: master
Change-Id: Ib34ae7fe4ac1e197af2183b8890cc72e13a900e9
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/60316


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Steffen Frese <steffenf14@gmail.com>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Steffen Frese <steffenf14@gmail.com>
Reviewed-by: Frank Naegler <frank.naegler@typo3.org>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>