[Sketcher] make more pointers to the UI std::unique_ptr

addendum to PR #4362

(Same as PR #4293, just for Sketcher

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 Sketcher dialogs that don't already use a unique_ptr.)

src/Mod/Sketcher/Gui/SketchRectangularArrayDialog.h

@@ -48,7 +48,7 @@ public:
 protected:
     void updateValues(void);
 private:
-    Ui_SketchRectangularArrayDialog* ui;
+    std::unique_ptr<Ui_SketchRectangularArrayDialog> ui;
 };
 
 }