[mlir][shard,mpi][NFC] Add missing header (#179777)

Utils.h uses `mlir::mpi::CommWorldOp` w/o including the necessary header
(https://llvm.org/docs/CodingStandards.html#self-contained-headers),
making this not self contained. It only works because all the .cpp files
that use it have the necessary include.

GitOrigin-RevId: 2e429f7e1f5b490a703de4cf06ef65eed784f7ab