More attachment errors could include the attachment index

There is a handy `enum AttachmentErrorLocation` that provides information about which attachment is problematic. It is used with several variants of `RenderPassErrorInner` (e.g. `UnsupportedResolveTargetFormat`), but not with `RenderPassErrorInner::ColorAttachment(ColorAttachmentError)` (nor is it used within `ColorAttachmentError`). The string for `AttachmentErrorLocation` is `{color/depth} attachment at index {index}'s texture view`, which I think is correct for the places it is used now, but would not be correct for all of the `ColorAttachmentError` cases, because some of those are about attachment attributes that don't directly correspond to a property of the texture view.