message: Add SCCP pass to MLIR bridge pipeline.
  This enables constant folding across function boundaries.
diff: @@ -294,6 +294,9 @@ void CreateConvertMlirToXlaHloPipeline(
  // with a tuple argument which break the assumption of resource lifting
  // inside PromoteResourcesToArgs.
  pm.addPass(mlir::mhlo::createLegalizeTFControlFlowPass());
  + // The SCCP pass performs constant propagation across the IR, which, for
  + // example, propagates constant arguments into callee functions.
  + pm.addPass(mlir::createSCCPPass());
  pm.addNestedPass<mlir::FuncOp>(mlir::mhlo::createLegalizeTFPass(
  /*allow_partial_conversion=*/true, /*legalize_chlo=*/true,
  