[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).

Beginne beim Image-Makro und verfolge, wie type, sampled=false und .read/.fetch das generierte OpTypeImage beeinflussen. Prüfe, wie NonReadable emittiert wird und wie Leseoperationen erlaubt werden. Erledigt ist dies, wenn ungültige nicht gesampelte Storage-Images als NonReadable markiert werden und nicht gelesen werden können, sofern dies nicht ausdrücklich aktiviert wurde, wobei das Verhalten anhand der im Issue beschriebenen Vulkan-Regel geprüft wird.