Bug 1766311. Disable hardware encoders on non-Android. r=jolin

Chrome has had a variety of issues with hardware encoders:
https://github.com/W3C/webrtc-extensions/issues/98#issuecomment-1054005251

We'll disable hardware encoders for now so that we can get consistent
behaviour everywhere. Once we've updated to a modern libwebrtc we
can reenable them.

This also makes it so that we can get resolution scaling on H264 without having
to cherrypick patches from upstream libwebrtc.

Differential Revision: https://phabricator.services.mozilla.com/D144773

modules/libpref/init/StaticPrefList.yaml

@@ -9623,7 +9623,7 @@
 
 - name: media.webrtc.platformencoder
   type: RelaxedAtomicBool
-#if !defined(MOZ_WIDGET_GTK)
+#if defined(MOZ_WIDGET_ANDROID)
   value: true
 #else
   value: false