[BUGFIX] Allow more tags when no RTE processing is available

If somebody has no RTE extension available, there is also no
RTE processing information available, so the default
from RteHtmlParser is used. However, tags like <abbr>
are then not provided by the yaml configuration, so they are
not allowed, and thus - escaped.

The patch adds abbr,acronym and dfn to be allowed all the time.

Resolves: #83424
Releases: master, 8.7
Change-Id: Ifdc0e7f155bef95a7c397584f2cf7b1eab61f6bb
Reviewed-on: https://review.typo3.org/58745


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Jürgen Heym <juergen.heym@hof-university.de>
Tested-by: Jürgen Heym <juergen.heym@hof-university.de>
Reviewed-by: Susanne Moog <susanne.moog@typo3.org>
Tested-by: Susanne Moog <susanne.moog@typo3.org>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>