media3 integration, handle audio focus gain/lost

[ghost]

Media3 pros:

• same player interface, which ease switching from playing in activity to playing in service
• out of the box integration with wear watches, google assistant, bluetooth headset etc. (by implementing mediasessionservice)
• exoplayer as core, so switching from exoplayer is straightforward

Cons:

• Need to refactor
• New bugs, such as crashing when playing in mediasessionservice. (which forces to use media metadata+medialibraryservice+mediaitemfiller).

[Skyyo]

all is clear, thanks for the research @ahamula . Seems media3 really doesn't provide anything of use now. Maybe we'll go for it when we need something with wear os, but even then we'll need to compare it with alternatives. Possibly they will force this upon us and deprecate the ExoPlayer.