Bug 1700473 [wpt PR 28196] - Switch ImageDecoder over to new ImageTrack semantics...

Bug 1700473 [wpt PR 28196] - Switch ImageDecoder over to new ImageTrack semantics., a=testonly

Automatic update from web-platform-tests
Switch ImageDecoder over to new ImageTrack semantics.

This moves frameCount and repetitionCount onto the track properties
and removes selectTrack() in favor of "track.selected = true". The
tracks list is modeled after Audio/VideoTrackList, but for now does
not include any events.

This also hardens the 'animated' status on a track so that it won't
change after metadata has been retrieved. repetitionCount is switched
to a 'unrestricted float' so 'Infinity' can be be accurately signaled.

R=chcunningham

Bug: 1182435, 1183456
Test: New and updated unittests and wpt tests.
Change-Id: Ibf8363e6f80d998202d42f745180812953681da9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2783220
Auto-Submit: Dale Curtis <dalecurtis@chromium.org>
Commit-Queue: Chrome Cunningham <chcunningham@chromium.org>
Reviewed-by: Chrome Cunningham <chcunningham@chromium.org>
Cr-Commit-Position: refs/heads/master@{#866786}

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wpt-commits: 8c208d775e1bcac4b6a9635f9f2484f9f10e8036
wpt-pr: 28196