Missing Window.Remove(control) and Window.CountControls()

Window exposes Add(control) but has no matching way to remove a child control at runtime, and no way to inspect how many direct child controls were currently attached.

Expected API:

Self.Remove(bt)
Var count As Integer = Self.CountControls()

Fix should add:

• Window.Remove(control As Control): removes a direct child control from the window and allows it to be added again later.
• Window.CountControls() As Integer: returns the number of direct child controls currently added to the window.