Window.FocusedControl returns the focused control

Add a read-only Window.FocusedControl As Control property for desktop applications. It returns the Objo control that currently has keyboard focus within that window, or Nothing when no Objo control has focus. This lets shared routines inspect the current input target without each application maintaining its own focus tracker. The returned value is the actual control instance, so callers can inspect its type, name, tag, and other members.