[BUGFIX] Reveal invisible soft hyphen character in CKEditor

This enables an editor to see where he added the 'soft hyphen' character
by switching to the source mode of the Rich Text Editor. The otherwise
invisible Unicode character is then replaced by the HTML entity '­'.

Resolves: #85391
Releases: master, 9.5
Change-Id: Idb8a6b554a068398abd7d788d30092ab16e6c668
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/57687


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Susanne Moog <look@susi.dev>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Susanne Moog <look@susi.dev>
Reviewed-by: Benni Mack <benni@typo3.org>