Bevy Lifecycle / simple rendering

[catilac]

The goal here will just be to make sure that we can have Bevy present to the surface managed by Processing.
Create the FFI code for driving the Bevy event loop, the idea here will but that each logical "frame" we'll drive the Bevy event loop forward one or more ticks (i.e. run the Main schedule) as well as figure out how to feed and map any user input events into the ECS. This probably isn't strictly necessary at first as we won't be writing too many of our own user-responsive systems in Rust, but could be useful for things like render picking in the future. I think this will be the first step in which we stub out a class for WebGPU that extends PGraphics