Gpuweb: Reconsider the name `OUTPUT_ATTACHMENT`

[Kangz]

OUTPUT_ATTACHMENT was an artefact of the initial import+rewrite of NXT's interface because NXT tried to have Vulkan-like render passes with sub-passes. It doesn't seem like WebGPU will have INPUT_ATTACHMENT in the near future, so maybe OUTPUT_ATTACHMENT should be renamed to RENDER_TARGET or an other name open to bikeshedding?

[kvark]

I think RENDER_TARGET is cleaner. It does however has a downside that generally people assume "color" targets. OUTPUT_ATTACHMENT doesn't have this problem, and it matches with the current names of other structs, such as GPURenderPassColorAttachmentDescriptor.

[Kangz]

That's a good point, maybe it could be RENDER_ATTACHMENT?

[kainino0x]

Resolution: "Resounding silent agreement"

[kvark]

Fixed by #1168