[SPIR-V 1.4] Deprecate OpDecorationGroup, OpGroupDecorate, and OpGroupMemberDecorate

[vmaksimo]

No description provided.

[LU-JOHN]

Maybe re-write as:

"OpGroupDecorate and OpGroupMemberDecorate are deprecated starting from SPIR-V 1.4"

[bashbaug]

Note, in the SPIR-V spec deprecation doesn't mean removal: https://registry.khronos.org/SPIR-V/specs/unified1/SPIRV.html#_deprecation

Additionally, it doesn't appear that the SPIR-V validator flags a SPIR-V 1.4 module using these instructions as invalid.

I think it would be fine to identify use of these deprecated instructions with a warning, but failing translation seems a bit too strong.

[vmaksimo]

I think it would be fine to identify use of these deprecated instructions with a warning, but failing translation seems a bit too strong.

@bashbaug I agree, but unfortunately for now we don't have a mechanism to report a warning in llvm-spirv (am I wrong?).
If so, I think that maybe it'd be a solution to just ignore and close this PR, as it does not change much.