Close stream when idle on Android

[chatziko]

Since recently (#931), snapclient on pulseaudio closes the stream when idle. This awesome little change reduced the idle CPU usage on my PI4 from 5-10% to almost 0.

So I wondered whether the same optimization is performed on Android (oboe/opensl), but as far as I can tell from the code (not an expert), it is not. On my phone snapclient seems to take 1-2% cpu when idle, not too much, but still on mobile devices we also have the battery to worry about.

It would be great if the close-when-idle optimization could be implemented on Android.