NFC: Make hlsl::IntrinsicOp enum values stable (microsoft#7231)

This change makes hlsl::IntrinsicOp enum values stable by:
- adding hlsl_intrinsic_opcodes.json to capture assigned indices
- adds this to the files generated by hctgen
- generation assigns new indices after the last index
- hlsl::IntrinsicOp enum values have explicit assignments
- removes ENABLE_SPIRV_CODEGEN ifdefs around opcode definitions and
lowering table entries to keep these stable whether or not the spirv
build setting is enabled.

Fixes microsoft#7230

Author: tex3d

CMakeLists.txt

@@ -686,6 +686,8 @@ add_subdirectory(include/dxc)
 # really depend on anything else in the build it is safe.
 list(APPEND LLVM_COMMON_DEPENDS HCTGen) 
 
+add_subdirectory(utils/hct)
+
 if(EXISTS "${LLVM_MAIN_SRC_DIR}/external")
   add_subdirectory(external) # SPIRV change
 endif()