Sanity warnings (WIP 🚧)

[jhvst]

It would be nice to add some sanity warnings for compute shaders.

To start with:

1. Emit a warning if shader has a constant LocalSize on x-dimension less than the current subgroup size. Otherwise each invocation in the shader will be treated as a new subgroup, which makes use of subgroup operations impossible. In more abstract sense, this is a problem in the unclear semantics of what is a LocalSize in a shader and what is client side cmd_dispatch dimension, and how these two interact together.