Added OpenGL support on Android

[jp2masa]

What does the pull request do?

• Added OpenGL support on Android.

What is the current behavior?

There's no hardware acceleration on Android.

What is the updated/expected behavior with this PR?

OpenGL is enabled on Android by default. Control Catalog is no longer too slow on Android, but still a bit slow.

Checklist

• Added unit tests (if possible)?
• Added XML documentation to any related classes?
• Consider submitting a PR to https://github.com/AvaloniaUI/Avaloniaui.net with user documentation

[kekekeks]

I guess the only thing left is to make it work from a background thread so DeferredRenderer could do its thing

[jp2masa]

I believe that as well, unfortunately I don't know exactly how it works. If you could point me in the right direction I would be thankful, but don't be bothered to explain if it's too complex.

[kekekeks]

It's actually pretty simple

1. implement IRenderTimer that ticks on the background thread and is synchronized with the display refresh rate (or use SleepLoopRenderTimer for now), pay attention to not trigger ticks when app is in background
2. change the renderer to DeferredRenderer and set RenderOnlyOnRenderThread to true
3. add the relevant locks

That's a story for a different PR though