Android: Opt out of back invoked callback

When 9d9b6d8 changed our target SDK version to Android 16, it made
Android 16 stop calling onBackPressed and stop delivering KEYCODE_BACK
events. Dolphin's code isn't ready for that yet.

Android lets us opt out of this new behavior for now, so let's do so.
But the opt-out will presumably stop working once we start targeting
Android 17, so we're going to have to update Dolphin's code within the
next one or two years to support the replacement API.

When Android sends Dolphin to the background, emulation *must* pause,
otherwise emulation continues running and continues outputting audio to
the user. RetroAchievements mustn't be allowed to override it.

Android: Show input indicators in controller settings

Android: Ask system for optimal audio buffer size and sample rate

Without this, there was a bug where if you turned the device's screen
off and on again while in the advanced mapping dialog, the input
indicators would stop updating. This is because turning the screen on
again causes devices to refresh, which causes all devices to be
recreated, leaving the AdvancedMappingControlViewHolders stuck
referencing controls belonging to devices that are no longer being
updated.

This makes sure view holders get proper widths when they use
layout_width="match_parent". This becomes quite noticeable for
AdvancedMappingControlAdapter in the next commit, but I'm also
making the change for other adapters while I'm at it.