iOS: Responding to Actions via UIAccessibilityAction

Description

There are actions that a VoiceOver user may invoke while using an application. React Native should be able to respond to these actions. One example that is currently missing from React Native's support is accessibilityScroll, which typically is listened to in order to perform a scroll action on a list of some kind.

React Native version:

v0.63

Expected Behavior

There is already precedent in React Native for actions, so in theory all the "actions" available for iOS would have associated functions. For scrolling, something like "onAccessibilityScroll(direction:)" would be called when the gesture is detected by the system.

iOS Details

UIAccessibilityAction is an informal protocol which contains instance methods to override. Ideally, all of the supported actions would be bridged.

まず、React Native に既存のアクセシビリティアクション処理と、issue にリンクされている UIAccessibilityAction のドキュメントを確認し、具体例として accessibilityScroll を使用します。ネイティブから JavaScript へのエントリーポイントと、既存のアクションの前例を特定し、次に、サポートされている iOS アクションを VoiceOver から呼び出せること、およびアプリケーションに公開できることを確認します。