[PiP] Use new functions expose by Element Call about PiP

[bmarty]

Element Call is exposing 3 new functions about PiP:

• canEnterPip: will return a boolean to let the application if it is possible to enter the PiP mode. If the call is in error state for instance, the application should not enter PiP but rather hang up the call. So if this function return true: enter PiP, else close the call.
• enablePip to be called when the Activity is entering PiP, and will let Element Call render the PiP mode correctly
• disablePip to be called when the Activity is exiting PiP, so render in fullscreen, and will let Element Call render the fullscreen mode correctly

Ref: element-hq/element-call#2573

[pixlwave]

For your reference, this is where we're using the API on iOS:

https://github.com/element-hq/element-x-ios/blob/dad9618f59c7494dbc69c150f2d71856c1d97c00/ElementX/Sources/Screens/CallScreen/View/CallScreen.swift#L211-L259

And if that requestPictureInPicture method fails we then decide to navigate back to the previous screen.