feat: Add support for Document Picture-in-Picture

[beaufortfrancois]

This PR adds experimental support for the Document Picture-in-Picture API in the Shaka Player.

I'm making some assumptions about how Shaka Player works and I'd love your review on this. Thank you!

Closes #4964

[avelad]

@beaufortfrancois Please, fix the build errors. Thanks!

[avelad]

I've been testing the functionality, several things I've seen:

• The dimensions that the player occupies in the window becomes 0, this can cause problems in some websites.
• The label of whether you are in PiP mode or not PiP is not updating correctly.
• Missing to detect if the functionality is allowed (see isPipAllowed_)

[beaufortfrancois]

• The dimensions that the player occupies in the window becomes 0, this can cause problems in some websites.

I agree and that's something I'd like to discuss. Adding a container may be enough. I'm not sure though.

• The label of whether you are in PiP mode or not PiP is not updating correctly.

Fixed. Thanks!

• Missing to detect if the functionality is allowed (see isPipAllowed_)

I forgot to upload that change earlier. Thank you!

[github-actions]

Incremental code coverage: 23.68%

[avelad]

• The dimensions that the player occupies in the window becomes 0, this can cause problems in some websites.

I agree and that's something I'd like to discuss. Adding a container may be enough. I'm not sure though.

@joeyparrish , what is your opinion about that?

[avelad]

LGTM!

[joeyparrish]

Looks like the externs for documentPictureInPicture need to be updated to make that an implementation of EventTarget. I'll make the revision.

[joeyparrish]

Some other type information is missing, too, so I'm adding all of it.

[beaufortfrancois]

@joeyparrish Thanks for fixing externs!

[beaufortfrancois]

Do you folks know when this feature will be available in next shaka player release?

[beaufortfrancois]

@joeyparrish @avelad
Do you know which release will have Document Picture-in-Picture support? Any rough ETA?