`wgpu::Buffer` implementing `PartialEq`, `Eq`, and `Hash` about wgpu

[kpreid]

It makes sense to me that every wgpu type that has an ID should be comparable by that ID.

[cwfitzgerald]

Yeah global ids aren't going away any time soon, so I think it's reasonable to have these

[dfellis]

So I am a bit stumped on how to test this. I have implemented the traits for Buffer but as there's no constructor for the type, I'm at a bit of a loss as to how to write unit tests.

If you have any suggestions, let me know, then I'll look for other types that have an id and add the traits for those, as well.

[Wumpf]

@dfellis have a look at the tests under wgpu/tests. They come with a test framework that makes it easier to create buffers from a device. A bit overkill on one hand but otherwise we'd need to start mocking things which gets complex (and we might just do that in that very framework if we ever figure that device creation etc. is too slow for tests that should only validate things like this)