Support for WASM/WASI + non-browser, non-JS, non-emscripten environments

[sunny-g]

I'll spare the preamble and just get to the point: it'd be really great to be able to use WGSL + wgpu (and the crates that depend on them) in a WASI or similar server-like environment to abstract away differences in GPUs and shader languages. There is no "official" proposed specification for WebGPU in WASI, so this is probably a moonshot until then, and I started work on this only to find out that changes would ripple across nearly all wgpu-* crates, and so put it aside until this discussion could be had.

What would be needed:

• (if adopting the WASM Component Model) a WIT definition derived from the webgpu.h header or WebGPU WebIDL
• an additional wgpu-hal::Instance which would be enabled in wasm32, non-emscripten environments and (in the guest WASM) would be simply makes calls to the bindings
• a host implementation (for wasmtime, wasmer, etc) that mediates between the bindings and either wgpu directly or wgpu-native

Nice to haves:

• tree-sitter or similar tool to automatically sync changes in webgpu.h to the WIT definition
• an explicit proposal to add WebGPU

Upsides:

• projects like burn and downstream crates that build onwgpu would "just work" when compiled to wasm32-wasi executed by a webgpu-enabled runtime
• source code for games/visualizations/etc could be compiled to run outside the browser (via winit, or a similar WASM Component stub library)

Downsides:

• might introduce a premature maintenance burden, as efforts to standardize WebGPU without JS seem non-existant

Alternatives:

• I/someone could just roll out a WASM component that mimics the web_sys::Window and wgpu APIs, though that has its own maintenance burden
  • also, without nearly-identically copying the informal wgpu crate API, wgpu-dependent crates wouldn't be patch-able
• ... perhaps there's an easier, less intrusive way? Open to suggestions

Anyways, I hadn't yet seen a singular issue/discussion/etc anywhere regarding wgpu + WASI (aside from bytecodealliance/wit-bindgen#175), and so this might be a bit off-base regarding the actual requirements to implement this, but I thought it worthy to create it here to at least initiate the discussion.

Additional links:
https://github.com/WebAssembly/wasi-webgpu
https://github.com/MendyBerger/wasi-webgpu