FCE-321: iOS camera in background; FCE-1727: Add PiP support to mobile-sdk

[MiloszFilimowski]

Description

• Picture in Picture. Displayes main and secondary tracks if available, secondary track is determined by VAD.
• On iOS support for background camera while in PiP

This is still a bit of an ongoing effort. UI and track switch should be improved in next PRs. This PR introduces the main concept which works.

Motivation and Context

• Customers need PiP when dealing with calls in background

Documentation impact

• Documentation update required
• Documentation updated in another PR
• No documentation update required

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to
  not work as expected)

[linear]

FCE-321 iOS camera in background

[linear]

FCE-1727 Add PiP support to mobile-sdk

[anna1901]

I've tested it and it works great! I just noticed two issues on android, but maybe they can be handled in the next PR:

1. The video is stretched horizontally in the PIP view
2. When I'm on a call and then I leave the app and I can see the pip, then when I return to the app the video from the camera is not centered as before, but it is moved to the leading edge of the video view.

[MiloszFilimowski]

I've tested it and it works great! I just noticed two issues on android, but maybe they can be handled in the next PR:

1. The video is stretched horizontally in the PIP view
2. When I'm on a call and then I leave the app and I can see the pip, then when I return to the app the video from the camera is not centered as before, but it is moved to the leading edge of the video view.

Thank you! I'm going to handle this in FCE-2148