[TASK] RTE: Rename "acronym" plugin and button to "abbreviation"

The acronym tag being deprecated, the RTE "acronym" plugin and button
are renamed to "abbreviation".

Releases: master
Resolves: #54409
Change-Id: I7b8335e6aac298650f83055e060c752d0d896038
Reviewed-on: http://review.typo3.org/33993
Reviewed-by: Stanislas Rolland <typo3@sjbr.ca>
Tested-by: Stanislas Rolland <typo3@sjbr.ca>