withPanelDirection function
Wraps child in the Directionality direction resolves to,
unconditionally — not a host opt-in (design spec, "Flutter").
Every screen wraps its whole returned widget (Scaffold included), not
just the body, so the app bar — title alignment, the back button's side —
follows the panel's own layout too.
Implementation
Widget withPanelDirection(PanelDirection direction, Widget child) {
return Directionality(
textDirection: textDirectionOf(direction),
child: child,
);
}