Hide controls when animating in and out of PiP

[defagos]

As a user I want a nice experience when animating in and out of PiP.

Acceptance criteria

• Controls are hidden when transitioning from / to PiP.

Tasks

• Publish state from PictureInPicture.
• Hide UI in demos implementing PiP when transitioning.
• Avoid showing controls when returning from PiP.
• Return isPossible as false when transitioning out of PiP? (would avoid button flickering)

[defagos]

Not really relevant anymore. Apps can use our PictureInPictureButton which uses these states internally. No need to hide controls during animation as well since we could implement very fast transitions in and out of PiP.