Validate storage buffer access

[teoxoy]

Storage buffers only support read or read_write access modes (not write).

Related: gfx-rs/wgpu#4411, gfx-rs/wgpu#3984

[ErichDonGubler]

A gray checkmark for you, sir!

[teoxoy]

@JCapucho how do you feel about this change in the context of GLSL? Do people qualify their buffers as writeonly? I'd imagine it's quite niche.

[JCapucho]

@JCapucho how do you feel about this change in the context of GLSL? Do people qualify their buffers as writeonly? I'd imagine it's quite niche.

I did see one shader at one point that used it, but yes, it seems like a quite niche thing.

Also I did some little research and it seems that writeonly is more of an hint gpuweb/gpuweb#935, I also took a glance at the vulkan and OpenGL specifications and it doesn't seem to be part of any validation for buffers.

I think this can be removed for now, and then emulated later in the glsl frontend.