TrackID has been used to denote tracks that are part of MediaStreams in the
MediaStreamGraph. The TrackInfo::mTrackId IDs are no longer used in the
MediaStream APIs and as such it's not necessary that they have the type TrackID.
This patch changes TrackInfo::mTrackId to be of type uint32_t instead, as that
is the type of Mp4parseTrackInfo::track_id, which is assigned to
TrackInfo::mTrackId as the sole remaining non-static user.
Other users set a static trackId of `1` or `2`, and as such remain supported by
this change.
Differential Revision: https://phabricator.services.mozilla.com/D46763
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extra : moz-landing-system : lando
9ed4e1aa58