Media element: Video player, Audio player and Flow player broken

[georgringer]

The swf files for the different media players can not be loaded in the frontend because of broken paths.

How to reproduce:
Install EXT:mediace
Create Media Content Element
Reference a video file from your local file system
=> Frontend is broken because flvplayer.swf can not be loaded. http://shots.michaelsen.io/I7yc

The issue occurs because the typoscript paths to these files were changed from "typo3/contrib/[...]" to "EXT:mediace/[...]" but the EXT: syntax is never resolved.

copy of https://forge.typo3.org/issues/67530