The "mediaClass" property now only serves to capture the original class
found on the media so that it can be roundtripped without causing dirty
diffs. In the 2.4.0 version of Parsoid's output, that will still be
the usual Image/Audio/Video. As of 2.5.0, it will always be File and
the mediaClass property can be dropped.
Parsoid is currently forward compatible with serializing mw:File, so
edited or new media can use that type already.
The contextmenu item for media has been updated to make use of the
"mediaTag" instead of mediaClass to continue distinguishing media types.
That was the only place a grep of mediaClass turned up any use.
Bug: T273505
Change-Id: If5dc6b794dacd6973d3b2093e6b385591b91d539
