[iOS] Prevent crash when setting cursor style

[m-bert]

Description

If you try to set cursor style in our buttons on iOS you'll get unrecognized selector error. This PR sets cursor value to be undefined on iOS, so apps no longer crash.

Fixes #3081

Test plan

Tested on the following code:

import React from 'react';
import { StyleSheet, Text, View } from 'react-native';
import { RectButton } from 'react-native-gesture-handler';

export default function EmptyExample() {
  return (
    <View style={styles.container}>
      <Text>Hello World!</Text>

      <RectButton
        style={{
          width: 100,
          height: 20,
          backgroundColor: 'blue',
          cursor: 'grab',
        }}
      />
    </View>
  );
}

const styles = StyleSheet.create({
  container: {
    flex: 1,
    justifyContent: 'center',
    alignItems: 'center',
    backgroundColor: '#F5FCFF',
  },
});