Fix thread safety of RNGestureHandlerModule methods

[jakub-gonet]

Description

Fixes #1169.

Another instance of changing the handler state outside the UI thread. In this case, calling handler.cancel() which calls mOrchestrator.onHandlerStateChange() interfered with scheduleFinishedHandlersCleanup() method which calls handler.reset() and sets mOrchestrator to null.

This may happen when threads interleave in the way described below:

1. RNGestureHandlerModule.dropGestureHandler is called (directly or in attachGestureHandler(); it's called on native modules thread)
2. RNGH dispatches first onStateChange event on UI thread
3. after dispatching event mHandlingChangeSemaphore is zero and call to scheduleFinishedHandlersCleanup() causes cleanupFinishedHandlers() to reset handlers and clear mOrchestrator
4. Native modules thread continues with execution and tries to call moveToState which crashes the app

This may show when RNGestureHandlerModule.attachGestureHandler() or RNGestureHandlerModule.dropGestureHandler() is rapidly called from JS (e.g. when frequently unmounting or updating handler component).

After checking the call hierarchy of GestureHandler.moveToState() it seems like this is the last occurrence of a native-module-calling-UI-only-method problem.

Example

Fast clicking on the TapGestureHandler crashes with error "Expected to run on UI thread", introduced in #1171. After applying this patch, the error disappears.

import React, { useState } from 'react';
import { View } from 'react-native';
import { TapGestureHandler } from 'react-native-gesture-handler';
export default () => {
  const [i, setI] = useState(0);
  const updateState = () => setI(i + 1);
  return (
    <View style={{ flex: 1, alignItems: 'center', justifyContent: 'center' }}>
      <TapGestureHandler onHandlerStateChange={updateState} key={i}>
        <View style={{ height: 100, width: 100, backgroundColor: 'pink' }} />
      </TapGestureHandler>
    </View>
  );
};

[kmagiera]

👍