Replace ImageAccess::descriptor_layouts()

[Rua]

Changelog

### Breaking changes
- The `buffer_with_range(_array)` constructor of `WriteDescriptorSet` now takes `DescriptorBufferInfo` structs.
- Removed the `descriptor_layouts` method on the `ImageAccess` trait. All images by default now use the `General` layout for storage image descriptors, and `ShaderReadOnlyOptimal` for all other image descriptors.

### Additions
- Added `image_view_with_layout(_array)` and `image_view_with_layout_sampler(_array)` constructors to `WriteDescriptorSet`, which let you control the image layouts used for image views bound to a descriptor.

This gets rid of one of the last methods of ImageAccess, to help with the image unification. The image layout is now included in the WriteDescriptorSet element definitions, and there's new constructors to specify it.

[marc0246]

The issue with trying stay close to Vulkan is that VkDescriptorImageInfo is a union in disguise. So we can't model it after the original API, at least not in any idiomatic capacity. There's a lot of inconsistency now with when info-structs are used and when not. I've been thinking about it for a while but I'm not sure what the best approach is.

[Rua]

I solved it in the end by making image + sampler a tuple of DescriptorImageViewInfo and Arc<Sampler>.

[marc0246]

Yes, but that's the inconsistency I'm talking about. :p