pub(crate) fn calculate_popup_dimensions(frame: Rect, window: &dyn KeyHandler) -> Rect {
        window.dimensions().map_or_else(Rect::default, |dimensions| popup_rect(dimensions, frame))
    }
Calculates the dimensions of the popup that is being focused. Currently used in
[`calculate_dimensions`](Self::calculate_dimensions) and
[`set_focused_window`](crate::app::Application::set_focused_window)
since the dimensions are constant and are only changed when the popup changes.

In the case that window is a an editor and not a popup, returns the default Rect,
which is essentially not displayed at all.
src/screen.rs