[TASK] Simplify markup of collapse buttons

We are removing the obsolete .collapseIcon
wrapper and replace the icons directly.

Resolves: #101854
Releases: main, 12.4
Change-Id: I7c640eba173edc167910312087c46d6614d7f5c1
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/80846


Tested-by: core-ci <typo3@b13.com>
Tested-by: Benjamin Kott <benjamin.kott@outlook.com>
Reviewed-by: Benjamin Kott <benjamin.kott@outlook.com>