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/Mod/Fem/Gui/ViewProviderFemConstraintDisplacement.cpp

@@ -70,8 +70,7 @@ bool ViewProviderFemConstraintDisplacement::setEdit(int ModNum)
 
 void ViewProviderFemConstraintDisplacement::updateData(const App::Property* prop)
 {
-    Fem::ConstraintDisplacement* pcConstraint =
-        static_cast<Fem::ConstraintDisplacement*>(this->getObject());
+    Fem::ConstraintDisplacement* pcConstraint = this->getObject<Fem::ConstraintDisplacement>();
 
     if (prop == &pcConstraint->xFree) {
         auto sw = static_cast<SoSwitch*>(getSymbolSeparator()->getChild(0));