[clang] [llvm] [clang][HLSL][SPRI-V] Add convergence intrinsics (PR #80680)

[Nathan Gauër via cfe-commits]

Keenuts wrote:

Thanks all the the reviews! We have 3 LGTMs and an ack from Arsenm, so I'm going to rebase on main, wait for the bots & tests, and if all is green, merge this.

https://github.com/llvm/llvm-project/pull/80680