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/MeshPart/Gui/CurveOnMesh.cpp

@@ -263,7 +263,7 @@ public:
     }
     void createGrid()
     {
-        Mesh::Feature* mf = static_cast<Mesh::Feature*>(mesh->getObject());
+        Mesh::Feature* mf = mesh->getObject<Mesh::Feature>();
         const Mesh::MeshObject& meshObject = mf->Mesh.getValue();
         kernel = meshObject.getKernel();
         kernel.Transform(meshObject.getTransform());

src/Mod/MeshPart/Gui/Tessellation.cpp

@@ -384,7 +384,7 @@ void Tessellation::setFaceColors(int method, App::Document* doc, App::DocumentOb
                 }
 
                 vpmesh->highlightSegments(diff_col);
-                addFaceColors(dynamic_cast<Mesh::Feature*>(vpmesh->getObject()), diff_col);
+                addFaceColors(vpmesh->getObject<Mesh::Feature>(), diff_col);
             }
         }
     }