Second screen android support

[DavidRGriswold]

Enable support for a second screen on android, either through a physical connection or using screen mirroring through Chromecast or Miracast.

What Currently Works

• A "Secondary Screen Layout" option has been added to the Settings menu on Android where user can choose between (1) System Default (mirroring) (2) Top Screen Only (3) Bottom Screen Only (4) Side by Side.
• A secondary window is always enabled at emulation start - either on an invisible virtual display or a physical display if it exists. If the setting is "System Default (mirroring)" the virtual display is used instead
• It is possible to switch back and forth between the virtual display and physical display using the settings above

Issues and changes yet to be done

• Test test test

Addresses #351

[rtiangha]

I'd be interested in seeing what the lag might be while casting. Might not matter much if the second screen is mostly static or not used often.

[DavidRGriswold]

I'd be interested in seeing what the lag might be while casting. Might not matter much if the second screen is mostly static or not used often.

The issue is that the most clear use-case involves casting the top screen while keeping the bottom touchscreen on the phone so touch input works as normal. So it would usually be the more active screen getting cast. It works pretty okay in my wifi environment - I wouldn't want to play, like, shovel knight on it, but it's okay for link between worlds type stuff where a little lag is unlikely to result in death.

that said, I think the most likely long-term use for this will be a two-screen android handheld, if such a thing ever comes to be. The DNA Duo on an Ayn Odin 2 basically makes one, but I expect a retroid pocket flip 3 with a smaller bottom screen between the controller parts in a few years.

[DavidRGriswold]

I am pretty sure this is ready for review or at least significant additional testing.

I have tested with vulkan pretty extensively - i have had a couple of crashes here and there but they are not consistently reproducible and I'm not even certain they can be linked to this code. That said there are almost certainly things that can be improved in the programming flow.

[DroidlyMobile]

I'd be interested in seeing what the lag might be while casting. Might not matter much if the second screen is mostly static or not used often.

Citra MMJ has the Media Projection library already integrated into it, and it's amazing to play on a secondary USB C display!!!! Even DNA Mobile Gaming has been developing/designing a detachable portable OLED display to use this!!!