SM6.10 implementation tracker: ClusterID and TriangleObjectPositions

- [ ] #7831 (includes valid-DXIL-pass test)
- [ ] DXIL Validation / invalid-DXIL-fail tests
- [ ] BuiltInTriangleHitPositions builtin type / tests
- [ ] HLSL gen_intrin_main.txt / sema tests
- [ ] HLSL -> DXIL lowering / lowering tests
