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.

首先查看 React Native 现有的无障碍操作处理方式，以及 issue 中链接的 UIAccessibilityAction 文档，并以 accessibilityScroll 作为具体示例。确定从原生到 JavaScript 的入口点和现有的操作先例，然后验证 VoiceOver 能够调用受支持的 iOS 操作，并将这些操作提供给应用程序。