[Core] Disable toggling visibility for objects

- VarSet
- Spreadsheet
- FEM objects

src/Mod/Fem/Gui/ViewProviderSolver.cpp

@@ -41,6 +41,7 @@ PROPERTY_SOURCE(FemGui::ViewProviderSolver, Gui::ViewProviderDocumentObject)
 
 ViewProviderSolver::ViewProviderSolver()
 {
+    setToggleVisibility(ToggleVisibilityMode::NoToggleVisibility);
     sPixmap = "FEM_SolverStandard";
 }