Combine the static Context and runtime (Compute/Render)Pass structs

[Pat-Lafon]

You shouldn't be allowed to mix and match a compute/render pass/pipelines. Moreover, a Context will never have any meaning without an accompanying pass to work on. So to avoid a lot of small cuts, the render pass should be merged into the Context.

There are probably a couple options to do this.

• We can expose the type of the Context to allow Context::new().
• A context can have a setter function which sets the pass of the context and makes it part of the type.
• I can accept a render/compute pass in eager_binding!
• Instead of setting context to some Context, I could instead set context to a closure that looks like |rpass| { Context{rpass} }