Implement effect asset compilation, loading and saving

Summary: This implements support for compiling, loading and saving MonoGame effects as EffectAssets.  Compilation is only supported on Windows platforms, but the effect assets can be cross-compiled to target other platforms (such as Linux).

Test Plan: Compiled some effect assets, saw them get loaded and used in the game successfully.

Reviewers: Sabre070

Reviewed By: Sabre070

Differential Revision: https://code.redpointsoftware.com.au/D134