Right-to-left layout and direction

Makes an Expo app correct in right-to-left languages on iOS and Android: screens mirror by themselves through logical styles, the layout direction is decided before the app starts and changes with exactly one guarded restart (never a loop), text reads in its own direction, physical surfaces and non-directional icons stay put, numbers show the language's digits, and a zero-dependency checker proves the code keeps it that way.

Rules that must hold