[Migrated] Image macro doesn't fully enforce valid use of non-sampled storage images

Issue automatically imported from old repo: https://github.com/EmbarkStudios/rust-gpu/issues/812
Old labels: t: bug,s: blocked
Originally creatd by fu5ha on 2021-11-29T20:17:40Z

Currently, if we create an image type with the image macro as such:

Image!(2D, type=f32, sampled=false),

the image will still be able to be .read/.fetched, and the spirv Image object won't be decorated as NonReadable. However, according to vulkan spec, "If shaderStorageImageReadWithoutFormat is not enabled, any variable created with a "Type" of OpTypeImage that has a "Sampled" operand of 2 and an "Image Format" operand of Unknown must be decorated with NonReadable."

This can be solved for now by just using an explicit format=blah in the Image macro instead of type, but I think we could also handle this/validate it in the macro automatically. I think the best way forward would be:

• Make a readable flag in the macro which gets auto-disabled under the above conditions, and when disabled, decorates the OpTypeImage with NonReadable and doesn't allow to do .read/.fetch on the Image.
• However, if it is manually enabled, then we do the current behavior, allowing read etc. (assuming shaderStorageImageReadWithoutFormat is enabled).

从 Image 宏开始，跟踪 type、sampled=false 和 .read/.fetch 如何影响生成的 OpTypeImage。检查如何发出 NonReadable，以及如何允许读取操作。完成标准是：无效的非采样存储图像被标记为 NonReadable，除非显式启用，否则无法读取，并根据 issue 中描述的 Vulkan 规则检查其行为。