Intent to ship: Matroska support

[Alastor Wu]

Starting with Firefox 145, Matroska (MKV) support will be enabled by default.

Matroska playback will be available for regular media playback only. However, support for Media Source Extensions (MSE) [1] and Media Recorder remains unavailable [2].

Bug: https://bugzilla.mozilla.org/show_bug.cgi?id=1991752
Pref: media.mkv.enabled
Platform coverage: All

Other browsers: Chromium-based browser supports Matroska, Safari does not.

[1] https://bugzilla.mozilla.org/show_bug.cgi?id=1988447

[2] https://bugzilla.mozilla.org/show_bug.cgi?id=1989491