Remove nested layers to avoid animation issues

[defagos]

Description

This PR fixes video view lagging animation issues we recently noticed when updating our Podcastator sandbox app.

Before	After
before.mp4	after.mp4

Changes made

• Use video layer as layer class of VideoLayerView.
• Update PiP implementation to store and restore a VideoLayerView instead of a layer.

Checklist

• APIs have been properly documented (if relevant).
• The documentation has been updated (if relevant).
• New unit tests have been written (if relevant).
• The demo has been updated (if relevant).