Emit when the active editor is changed.
Emit when the current editor is changed.
The active editor. If there is an active editor (one that has focus), active and current are the same.
The most recently activated editor (which might not have the focus anymore, hence it is not active).
If no editor has focus, e.g. when a context menu is shown, the active editor is
undefined, but current might be the editor that was active before the menu popped up.