message: Put a native back in the left menu bar
  Allows testing of back navigation and seems like the right place for it
diff: @@ -64,16 +64,32 @@ jest.mock('navigation-react-native', () => {
  });
  }
  - const NavigationBar = ({ title, children, ...props }) => (
  + const NavigationBar = ({ title, children, ...props }) => {
  + const Left = React.Children.toArray(children).find(({type}) => type === NavigationReactNative.LeftBar);
  + return (
  <ReactNative.View accessibilityRole="toolbar" {...props}>
  {!!title && (
  <ReactNative.Text accessibilityRole="header">{title}</ReactNative.Text>
  )}
  + {!Left ? <LeftBar /> : null}
  {children}
  </ReactNative.View>
  );
  + };
  - const LeftBar = (props) => <ReactNative.View accessibilityRole="menubar" {...props} />;
  + const LeftBar = ({children, ...props}) => {
  + const {stateNavigator} = React.useContext(NavigationReact.NavigationContext);
  + return (
  + <ReactNative.View accessibilityRole="menubar" {...props}>
  + {stateNavigator.canNavigateBack(1) && (
  + <ReactNative.Pressable accessibilityRole="menuitem">
  + <ReactNative.Text>Back</ReactNative.Text>
  + </ReactNative.Pressable>
  + )}
  + {children}
  + </ReactNative.View>
  + );
  + };
  const RightBar = (props) => <ReactNative.View accessibilityRole="menubar" {...props} />;
  