Allow non struct buffers in wgsl

[IcanDivideBy0]

Thanks to gfx-rs/naga@75692d3, it is now possible to use arrays top level components of a shader, this PR integrates the latest changes from naga to wgpu.

So far, it seems to work fine, but i'm still having an issue: when using the arrayLength builtin function on such an array (runtime sized), i have the following error:

thread 'main' panicked at 'wgpu error: Validation Error

Caused by:
    In Device::create_compute_pipeline
      note: label = `Particles pipeline`
    Internal error: module is not validated properly: array length expression

', /home/samuel/Workspace/wgpu/wgpu/src/backend/direct.rs:2273:5

I've tried to inspect the generated spirv but i'm not really familiar with this, any help appreciated.

[kvark]

Nice!

[IcanDivideBy0]

gfx-rs/naga#1717 definitely fixed the issue with arrayLength!