Add action changing focus from the selected element in Variable view to the equivalent in editors/animators and vice versa

Similarly to https://github.com/eclipse/gemoc-studio-modeldebugging/issues/127
When debugging a model execution, it would be interesting to have popup actions that go from the Variable view to the editors/animators (Xtext and/or Sirius) and vice versa (ie. select an element in the editors/animator and changes the focus to the corresponding element in the variable view)