Gui: Add getObject<T>() helpers to various classes

Obtaining specific kind of document object is very common task. This
commit introduces handy helper which makes that a lot easier.

src/Mod/Fem/Gui/ViewProviderFemPostFunction.h

@@ -65,10 +65,15 @@ protected:
     {
         return m_view;
     }
-    Fem::FemPostFunction* getObject()
+    Fem::FemPostFunction* getObject() const
     {
         return m_object;
     }
+    template<class T>
+    T* getObject() const
+    {
+        return dynamic_cast<T*>(getObject());
+    }
 
     bool blockObjectUpdates()
     {

src/Mod/PartDesign/Gui/TaskTransformedParameters.h

@@ -178,6 +178,9 @@ protected:
      */
     PartDesign::Transformed* getObject() const;
 
+    template <class T>
+    T* getObject() const { return dynamic_cast<T*>(getObject()); }
+
     /// Get the sketch object of the first original either of the object associated with this
     /// feature or with the parent feature (MultiTransform mode)
     App::DocumentObject* getSketchObject() const;

src/Mod/TechDraw/App/DimensionReferences.h

@@ -63,6 +63,7 @@ public:
     bool operator== (const ReferenceEntry& otherRef) const;
 
     App::DocumentObject* getObject() const;
+    template <class T> T* getObject() const { return dynamic_cast<T*>(getObject()); }
     void setObject(App::DocumentObject* docObj) { m_object = docObj; }
     std::string getSubName(bool longForm = false) const;
     void setSubName(const std::string& subName) { m_subName = subName; }