[windows] Implement a Win32/UWP version of the embedder

[stuartmorgan]

The current implementation on Windows is a temporary solution using GLFW; the goal is to implement a more flexible, view-based solution that could be used in an existing application, similar to what currently exists on macOS.

See previous discussion in issue #6.

[clarkezone]

I have been making good progress on a Win32/UWP implementation based on Angle. There are currently two engine changes blocking my fork: the first is a null reference exception in Dart. I have filed an issue on the Dart repo here dart-lang/sdk#33826 and developed a fix here: clarkezone/sdk@42f67a7.

The second is a change to Skia to make it delay load Angle. I need to clean up the code and will then prepare that next.

[weitzhandler]

WOW, this is great news.
The only reason I stand aside from Flutter is its lack of Windows support. I hope WASM support is also on the radar.

[stuartmorgan]

Moved to flutter/flutter#30726