Support bgra8unorm-storage extension #3359
Description
Prerequisite: gfx-rs/naga#2195.
Metal supports this.
DX12 optionally supports this (see gpuweb/gpuweb#3640 (comment)).
DX11 doesn't support this.
There is a possible workaround that we can implement if we want (see gpuweb/gpuweb#3640 (comment)).
Vulkan optionally supports this if the format supports STORAGE_WRITE_WITHOUT_FORMAT_BIT (see KhronosGroup/Vulkan-Docs#2027 (comment)).