[TASK] Add mapping between .pps, .ppsx and powerpoint

Add missing mapping between pps, ppsx
and the powerpoint application.

Resolves: #53833
Releases: 6.2
Change-Id: I9ecd8ec899bb24245326ca42a469ee41de9b2c79
Reviewed-on: https://review.typo3.org/27457
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters