[BUGFIX] Avoid stripping tags for generating diffs

Tags must not be stripped away for creating diffs as
those are essential for editors. Otherwise it is not
possible to see changed links or changing a header from
h1 to h2.

Resolves: #78767
Resolves: #79205
Releases: master, 7.6
Change-Id: Icb174f3522354fa8ef5d2b8ccca039e33ef472e7
Reviewed-on: https://review.typo3.org/51220


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>