Sketcher: Made constraints aware of whether they are dimensionals or not

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Centralise the knowledge on whether a constraint is dimensional or not within the constraint

src/Mod/Sketcher/App/Constraint.h

@@ -104,6 +104,9 @@ public:
     inline double getValue() const {
         return Value;
     }
+    
+    inline bool isDimensional() const { return Type == Distance || Type == DistanceX || Type == DistanceY ||
+                                         Type == Radius || Type == Diameter || Type == Angle || Type == SnellsLaw;}
 
     friend class PropertyConstraintList;