Allow outside audio while in-player mute is active

[J-Stutzmann]

Checklist

• I made sure that there are no existing issues - open or closed - which I could contribute my information to.
• I have read the FAQ and my problem isn't listed.
• I'm aware that this is a request for NewPipe itself and that requests for adding a new service need to be made at NewPipeExtractor.
• I have taken the time to fill in all the required details. I understand that the feature request will be dismissed otherwise.
• This issue contains only one feature request.
• I have read and understood the contribution guidelines.

Feature description

The player should not take audio focus while the in-player mute button is active.

To do this, the player should:

• Not Request audio focus on play, when player is muted
• Abandon audio focus on mute, when player is playing
• Request audio focus on unmute, when player is playing
• Not attempt to Request or Abandon audio focus when already in said state

In short, the player should Request audio focus only when moving into the "Playing + Unmuted" state, and Abandon it when moving to any other state.

Why do you want this feature?

In order to play audio from other apps while NewPipe is muted.

Additional information

N/A

[J-Stutzmann]

In addition, anyone looking to implement this should be aware that Play and onPrepared have separate audio focus requests.