Enable ImGui on Android.

[hysw]

ImGui renders, but the aspect ratio is wrong.
We should get the Android Window size instead of hard code 720p.

[apazylbe]

Is this enough to close #77? If that's the case, could you add Fixes https://github.com/google/bigwheels/issues/77 in the description (https://github.com/google/bigwheels/blob/main/CONTRIBUTING.md#for-developers-contributing-a-patch)

[hysw]

Is this enough to close #77?

Not yet, this only enable the rendering of ImGui, there's at least a few more things to fix:

• The surface size is wrong, so ImGui has a weird aspect ratio
• Still need to add input support
• The bigwheels Android event loop is broken (it's not processing Android input at all)

[apazylbe]

Thanks! I created 2 issues and assigned one existing to you, hope that's okay. If you are not planning to work on them, maybe you could add any relevant details and unassign?
Input handling: #78
Wrong surface size: #125
Event loop: #126

[hysw]

Okay, I'm actually have all three fixed on my local branch, so sounds more than reasonable to me (a earlier sample here: c2e4881 )