Test `importExternalTexture` with video frame display sizes and coded sizes from video file.

[haoxli]

If a video frame has different display sizes and coded sizes, importExternalTexture may throw validation errors and the external texture cannot be sampled correctly. This bug had been fixed in https://crbug.com/471021591, but the tests was missing.

The PR added the tests for a video frame from VideoFrame element. We would also prefer a version of these tests where the frame comes from a video file instead of a VideoFrame.