fix: appBar Accessibility Focus

[chewy444]

Motivation

Increase accessibility of Appbar.Content by adding support for Accessibilityinfo.setaccessibilityfocus allowing apps to focus screen readers on the Appbar.Content title when a screen is initially rendered.

Notes: Android requires the focused component to have accessible set in order to focus.

Example:

const FocusedHeader = () => {
  const ref = useRef<Text>(null);

  useEffect(() => {
    const handle = findNodeHandle(ref.current);
    AccessibilityInfo.setAccessibilityFocus(handle);
  });

  return (
    <Appbar.Header>
      <Appbar.Content
        titleRef={ref}
        title="Screen Title"
      />
    </Appbar.Header>
  );
};

Test plan

yarn flow && yarn typescript && yarn lint && yarn test

[callstack-bot]

Hey @chewy444, thank you for your pull request 🤗. The documentation from this branch can be viewed here.