Feature request: disable uniformity analysis on shader creation

[raphlinus]

Uniformity analysis of WGSL is too strict and fails to accept some valid shaders, including the coarse rasterization stage of piet-gpu. This is captured in an upstream WGSL bug and mitigations are being discussed. One such mitigation is to opt-out of the analysis.

I'd like a flag to disable uniformity analysis at shader creation time. That flag already exists in the naga API as ValidationFlags, but that's currently hardcoded to all() in wgpu-core's Device::create_shader_module() method, so basically what I'm asking is for that to be plumbed through.

The feature can be a temporary stopgap, and should probably be marked as such, until the issue is resolved upstream.

[ErichDonGubler]

@raphlinus: Would implementing the WGSL diagnostic filter management per #5320 satisfy this particular request? That's not the same as your request to expose this on the API side, but if you're willing to add diagnostic directives in shader source, this might be a standards-supported way to do this.