[clang] [HLSL][SPIRV] Add vk::binding attribute (PR #150957)

[Nathan Gauër via cfe-commits]

https://github.com/Keenuts commented:

LGTM, question around the default value. Seems like sema makes the default value be 0 as expected, so maybe the second template arg is not in fact the default value?

https://github.com/llvm/llvm-project/pull/150957