Make Fabric event receivers init only once

[szydlovsky]

Summary

Fixes #6896

When adding support for fabric, we have inadvertently kept previous listeners still active for fabric. This way, we registered twice with the same NodesManager for React Native's FabricEventDispatcher, resulting in pretty much all the events doubling in number on android. I added a simple check that takes care of it.

Test plan

Paste the following into EmptyExample and run FabricExample. Check logs making sure that both start and end are logged only once per gesture.

import React, { useState } from 'react';
import { View, Text } from 'react-native';
import Animated, { useAnimatedScrollHandler } from 'react-native-reanimated';

function EmptyExample() {
  const [w, sW] = useState(0);

  const scrollHandler = useAnimatedScrollHandler({
    onBeginDrag() {
      console.log('start');
    },
    onMomentumEnd() {
      console.log('end');
    },
  });

  return (
    <View
      style={{ flex: 1 }}
      onLayout={(evt) => sW(evt.nativeEvent.layout.width)}>
      <Animated.ScrollView
        onScroll={scrollHandler}
        horizontal
        snapToInterval={w}
        decelerationRate="fast">
        {Array.from({ length: 20 })
          .fill(0)
          .map((_, i) => {
            return (
              <View key={i} style={{ width: w }}>
                <Text>{i}</Text>
              </View>
            );
          })}
      </Animated.ScrollView>
    </View>
  );
}

export default EmptyExample;

[tomekzaw]

Code looks good to me, haven't tested it though, let's wait for approvals from other reviewers

[Titozzz]

Just had that issue pop up on android, so I'm happy for that PR to exist, keeping an eye on it

[piaskowyk]

I've tested it and it seems to work well 👍