[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/TaskLinearPatternParameters.h

@@ -85,7 +85,7 @@ private:
     void kickUpdateViewTimer() const;
 
 private:
-    Ui_TaskLinearPatternParameters* ui;
+    std::unique_ptr<Ui_TaskLinearPatternParameters> ui;
     QTimer* updateViewTimer;
 
     ComboLinks dirLinks;