[BUGFIX] Install Tool: Improve UX for foldout sections

Change the cursor and add an arrow for foldout sections
in the Install Tool.

Resolves: #49188
Releases: 6.2
Change-Id: Iaf8f17b420f0716a23b5a6d8d4ebbbaa815a9143
Reviewed-on: https://review.typo3.org/23755
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters
Reviewed-by: Jigal van Hemert
Tested-by: Jigal van Hemert