Internal b/150663666

Observe that when using TextField or TextFormField in Flutter on iOS platform, users cannot shift Accessibility Focus in VoiceOver once they're in editing mode.

Background: One of the criteria for A11y testing is that users should be able to swipe Left / Right / Up / Down gestures in VoiceOver mode regardless where they are.

Actual result: Users are stuck in TextField / TextFormField editing mode.

Steps to reproduce:

1. Turn on VoiceOver
   2a. Navigate to a screen that has a TextField or TextFormField
   (OR 2b. Navigate to a screen that has a TextField or TextFormField with autofocus: true)
2. Navigate to the TextField using swipe gestures
3. Double to focus on the TextField
4. Observe that swiping left / right / up / down doesn't shift a11y anymore