[mlir][transform] Expose transform op from TrackingListener

[springerm]

Summary

This allows subclasses (such as the ErrorCheckingTrackingListener in IREE) to produce better error messages.

mlir/include/mlir/Dialect/Transform/IR/TransformOps.h

protected:
   /// replacement op was found. Derived classes can implement this function for
   /// custom error handling.
   virtual void notifyPayloadReplacementNotFound(Operation *op,
                                                 ValueRange values) {}
 
   /// Return the single op that defines all given values (if any).
   static Operation *getCommonDefiningOp(ValueRange values);
 
+  /// Return the transform op in which this TrackingListener is used.
+  TransformOpInterface getTransformOp() const { return transformOp; }
+
 private:
   void notifyOperationRemoved(Operation *op) override;
 
   void notifyOperationReplaced(Operation *op, ValueRange newValues) override;
 
   /// The transform op in which this TrackingListener is used.
   TransformOpInterface transformOp;
 };
 
 } // namespace transform
 } // namespace mlir
 
 #define GET_OP_CLASSES
 #include "mlir/Dialect/Transform/IR/TransformOps.h.inc"
 
 #endif // MLIR_DIALECT_TRANSFORM_IR_TRANSFORMOPS_H