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/PartDesign/Gui/ViewProviderDatum.cpp

@@ -289,7 +289,7 @@ bool ViewProviderDatum::doubleClicked()
     Msg += this->pcObject->Label.getValue();
     Gui::Command::openCommand(Msg.c_str());
 
-    Part::Datum* pcDatum = static_cast<Part::Datum*>(getObject());
+    Part::Datum* pcDatum = getObject<Part::Datum>();
     PartDesign::Body* activeBody = activeView->getActiveObject<PartDesign::Body*>(PDBODYKEY);
     auto datumBody = PartDesignGui::getBodyFor(pcDatum, false);