[BUGFIX] HTML5: use self-closing tags only if allowed

For HTML5 only certain HTML tags are allowed to be self-closing
(e.g. <img src="..." />), so this needs to be checked when
parsing HTML.

Resolves: #78844
Releases: master, 8.7
Change-Id: If2a319fa83a4baf7d78559aa23ce34903d42d342
Reviewed-on: https://review.typo3.org/50812


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Mathias Schreiber <mathias.schreiber@typo3.com>
Tested-by: Mathias Schreiber <mathias.schreiber@typo3.com>
Reviewed-by: Jigal van Hemert <jigal.van.hemert@typo3.org>
Tested-by: Jigal van Hemert <jigal.van.hemert@typo3.org>