414: Implement MultiDrawIndirect Extensions r=kvark a=cwfitzgerald
The wgpu-rs component of https://github.com/gfx-rs/wgpu/pull/754.
I didn't include the modifications to the example as they are particularly awful and ugly. One of my next steps following this is to make an example of both binding indexing and these multi-draw extensions.
Co-authored-by: Connor Fitzgerald <connorwadefitzgerald@gmail.com>