Gui: Use getObject<T>() helpers in classes

This commit is generated using regex based find and replace:

```
s/[\w:]+_cast\s*<([^>]+)\*>\s*\(\s*getObject\(\s*\)\)/getObject<$1>/
s/[\w:]+_cast\s*<([^>]+)\*>\s*\(\s*([^)]*)\s*->\s*getObject\(\s*\)\)/$2->getObject<$1>()/
```

To regenerate if needed.

src/Gui/DlgAddPropertyVarSet.cpp

@@ -53,7 +53,7 @@ const bool COMMIT = false;
 DlgAddPropertyVarSet::DlgAddPropertyVarSet(QWidget* parent,
                                            ViewProviderVarSet* viewProvider)
     : QDialog(parent),
-      varSet(dynamic_cast<App::VarSet*>(viewProvider->getObject())),
+      varSet(viewProvider->getObject<App::VarSet>()),
       ui(new Ui_DlgAddPropertyVarSet),
       comboBoxGroup(this),
       completerType(this),