Android: Full '4K' support (i.e. without scaling)

[mark-kendall]

A recap of the issue:-

• Qt and/or Android virtualise the UI window when running higher than HD resolutions (1920x1080)
• so when using a 4K screen/mode, the UI and its associated OpenGL context are always created with a 1920x1080 surface
• during 4K video playback (for both software decode and MediaCodec accelerated) we still use 4K video textures but these are effectively downscaled to HD in our rendering before being scaled back up again when the Qt surface is finally rendered.
• the end result is that we lose full 4K rendering - despite the screen running at 4K

Some previous discussion:-

https://lists.archive.carbon60.com/mythtv/dev/619004

Prospective associated code for display res switching: #219

Possibly relevant updates to Qt:

1 - qt/qtbase@b2d24dc
This should be in current Qt and I'm not sure if it has been tested at any point.

2 - qt/qtbase@a35a7fc
This looks like it might be the winner (as it calls Display.getRealMetrics) but is not in any Qt release yet (patch our Qt version in the Android packager?)

Possibly relevant MythTV code:

• we set Qt::AA_DisableHighDpiScaling in MythDisplay::::ConfigureQtGUI
• in latest master (and backported to fixes/31), we now properly support High DPI settings on macOS. So if the second Qt update above behaves in the same way as macOS then we should be good to go... (N.B. that means the window system still uses the virtualised size (HD) but sets the devicePixelRatio to 2.0)