The patch simplifies and optimizes the readability of the page module
interface. It is based on the UX Team's concept of improving user
experience for editors:
https://typo3.org/article/structured-content-initiative-feedback-wanted

Included changes:

* refactored and optimised underlying CSS for future adaptions
* visually simplified content element boxes and their header buttons
* visually differenciated hidden content elements with better opacity
  and dotted border
* placed the "new content element" buttons centered in preparation
  for further concept implementations in dedicated patches
* added a new button for content element context menu in the content
  element header right button bar

This patch was initiated by the UX Team and implemented by Benjamin
Kott.

Resolves: #97306
Resolves: #95247
Related: #94629
Releases: main
Change-Id: I9b4e21a7fc68ebcb17d18f65bf00096f3a295cfb
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/74254


Tested-by: Benjamin Franzke <bfr@qbus.de>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Michael Telgkamp <michael.telgkamp@mindscreen.de>
Tested-by: Annett Jähnichen <mcmietz@web.de>
Reviewed-by: Benjamin Franzke <bfr@qbus.de>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Michael Telgkamp <michael.telgkamp@mindscreen.de>
Reviewed-by: Annett Jähnichen <mcmietz@web.de>