[PD] make pointers to the UI std::unique_ptr

Same as PR #4293, just for PartDesign

as noted in https://github.com/FreeCAD/FreeCAD/pull/4271#discussion_r554673632
the pointer to the UI should be a unique pointer.

This PR does this for all PartDesign dialogs that don't already use a unique_ptr.

src/Mod/PartDesign/Gui/TaskMultiTransformParameters.h

@@ -100,7 +100,7 @@ private:
     void finishAdd(std::string &newFeatName);
 
 private:
-    Ui_TaskMultiTransformParameters* ui;
+    std::unique_ptr<Ui_TaskMultiTransformParameters> ui;
     /// The subTask and subFeature currently active in the UI
     TaskTransformedParameters* subTask;
     PartDesign::Transformed* subFeature;