Constrain Areas to screen by default (#4591)

Call `area.constrain(false)` if you want your areas to extend outside
the screen rect.

crates/egui_extras/src/datepicker/button.rs

@@ -142,7 +142,6 @@ impl<'a> Widget for DatePickerButton<'a> {
             } = Area::new(ui.make_persistent_id(self.id_source))
                 .order(Order::Foreground)
                 .fixed_pos(pos)
-                .constrain_to(ui.ctx().screen_rect())
                 .show(ui.ctx(), |ui| {
                     let frame = Frame::popup(ui.style());
                     frame