Model: Autoplay and loop test

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If a model contains an animation track, it will be available to play once the model has loaded. autoplay will trigger the playback automatically, and loop will loop the content, irrespective of whether the playback was started via the JavaScript play() or the attribute.

<model autoplay loop alt="A model of a teapot with a hidden creature">
  <source src="./teapot.usdz" type="model/vnd.usdz+zip" />
  <source src="./teapot.glb" type="model/gltf-binary" />
</model>