requestVideoFrameCallback is missing from HTMLVideoElement

[jezell]

https://wicg.github.io/video-rvfc/

https://developer.mozilla.org/en-US/docs/Web/API/HTMLVideoElement/requestVideoFrameCallback

[jezell]

Corresponding cancellation function also missing:

https://developer.mozilla.org/en-US/docs/Web/API/HTMLVideoElement/cancelVideoFrameCallback

[srujzs]

Both should be added as part of #209, so deduping.

Duplicate of #209.