Implement enumerate_adapters for rs-backend

[dskkato]

I originally used wgpu with WebGPU, but recently I came across this library. As mentioned in #409, I also needed to choose an adapter to try out compute shaders, so I implemented it on a trial basis. I'm not sure if it conforms to your coding style, but I would appreciate it if you could review it. If you are already working on something similar, please feel free to close it as appropriate.

Resolves #409

[almarklein]

Really nice!

The codegen sometimes makes refactorings like this a bit tricky. I added a comment for a way to work around this.

I'm not 100% sure about the API, relates to #410. But the solution you offer here - to make the user go into wgpu.backends.rs - seems like a pretty good alternative. We'd have to figure out how to document this function though.

This also relates somewhat to #408. I propose that we move this PR forward and figure out the #401 stuff later.

[dskkato]

FYI: The example for wgpuInstanceEnumerateAdapters I referenced is this -> https://github.com/gfx-rs/wgpu-native/blob/trunk/examples/enumerate_adapters/main.c

[almarklein]

LGTM. This is going to be interesting merging with #408 😄 I propose we merge this into main and then I'll merge main into #408.

[almarklein]

Thanks for your contribution!

[almarklein]

For the record, when #408 is merged, it will be wgpu.backends.wgpu_native.enumerate_adapters().