Update [Custom Android back button behavior] example

Hi! I am currently refactoring code to using hooks. And I found refactoring the custom back button behaviour confusing.

I tried to adapt the example you have here to the code I refactored

import React from "react";
import { BackHandler } from "react-native";

const ScreenWithCustomBackBehavior = ({ navigation }) => {

const onBackButtonPressAndroid = useCallback(() => {
    if (isSelectionModeEnabled()) {
      disableSelectionMode();
      return true;
    } else {
      return false;
    }
  }, [isSelectionModeEnabled, disableSelectionMode]);

  useEffect(() => {
    const _didFocusSubscription = navigation.addListener('didFocus', () => {
      BackHandler.addEventListener('hardwareBackPress', onBackButtonPressAndroid);
    });
    const _willBlurSubscription = navigation.addListener('willBlur', () => {
      BackHandler.removeEventListener('hardwareBackPress', onBackButtonPressAndroid);
    });

    return () => {
      if (_didFocusSubscription) {
        _didFocusSubscription.remove();
      }
      if (_willBlurSubscription) {
        _willBlurSubscription.remove();
      }
    };
  }, [navigation, onBackButtonPressAndroid]);
}

  return (
    // ...
  )

Do you think it's a proper way to do it? If yes, should I submit a PR?

Thank you

审查链接的自定义 Android 返回按钮行为示例和提议的基于 hooks 的代码片段。决定是否应将示例更新为这种方式；完成意味着文档示例体现了已达成一致的行为，并且读者能够清楚理解。