Add partial support for khr_fragment_shading_rate

[LDeakin]

This adds partial support for khr_fragment_shading_rate.

• FragmentShadingRateState for GraphicsPipeline
• DynamicState::FragmentShadingRate and set_fragment_shading_rate
• Per-region support VkFragmentShadingRateAttachmentInfoKHR

Changelog:

### Additions
- Partial support for the `khr_fragment_shading_rate` extension.

[marc0246]

I think it looks wonderful!

[marc0246]

We should definitely add this to the task graph's command buffer (doesn't have to be in this PR), as any contribution to the old command buffer is instant legacy code. The old command buffer will be deprecated in the release after the next and eventually removed entirely together with GpuFuture.

[LDeakin]

This supports all but per-region fragment shading rate, which is a bit more involved. Perhaps a future PR?

[Rua]

Looks good! Could you add a short documentation to the top of the fragment_shading_rate module, describing what it does?

[LDeakin]

In writing the docs, I realised I don't validate that primitive_fragment_shading_rate is enabled for per-primitive shading. But, I could not find an associated VUID for that.

[marc0246]

Could you please format the validation messages like they are elsewhere? That is, use backticks around arguments/code and use line continuation to ensure they don't end up longer than 100 columns.

[marc0246]

It LGTM; I just have some nits remaining.

[marc0246]

Unfortunately, I don't have an answer for your earlier question. It looks as though there is no VUID specifically for primitive_fragment_shading_rate. There is the SPIR-V capability FragmentShadingRateKHR but it applies to all 3 device features; there is not one capability per device feature. I really wish there was, because this means that we do in fact have no way of validating them individually and the user has to know what they're doing :/

[LDeakin]

Thanks for reviewing and getting this in so quick @marc0246 and @Rua!