Remove magic number and hard type enums in ArrowPropEnum.h

- Remove currently present magic numbers
- Hard type enums, so magic numbers can no longer be introduced. We don't want people to introduce magic numbers.

src/Mod/TechDraw/Gui/DlgPrefsTechDrawAnnotationImp.h

@@ -31,6 +31,7 @@
 
 namespace TechDraw {
 class LineGenerator;
+enum class ArrowType : int;
 }
 
 namespace TechDrawGui {
@@ -53,7 +54,7 @@ protected:
     void loadSettings() override;
     void changeEvent(QEvent *e) override;
 
-    int prefBalloonArrow() const;
+    TechDraw::ArrowType prefBalloonArrow() const;
     int prefBalloonShape() const;
     int prefMattingStyle() const;
     void loadLineStyleBoxes();