UIManager::manageChildren arrays reconciliation support

[maxhora]

UIManager::manageChildren implementation introduces issues on some scenarios.

Possibly, it happens because input argument addAtIndices may contain any range of values to add new element at, but current implementation, seems, adds new items only to the end of parent containers list (QQuickItem API to insert new child at specific position seems is not available ? ):

child->setParentItem(container);

JS source sample with issues:

import React, { Component } from 'react';
import {
 AppRegistry,
 Alert,
 Text,
 TouchableHighlight,
 View,
 TextInput,
 Button
} from 'react-native';



class ItemList extends Component {
 constructor(props) {
   super(props);
   this.state = {longList: true};
   this.onPress = this.onPress.bind(this);
 }

 onPress() {
   this.setState({longList: !this.state.longList});
 }

 onButtonPress() {
  this.setState({longList: !this.state.longList});
 }

 render() {
   let items = this.state.longList ? ["Long11", "Long22", "Long23"] : ["Long22", "Long23"];
   return (
     <View onPress={this.onPress}>

       <View>
       {items.map(function(name, index) {
         return <Button key={name} title={name} > </Button>;
       })}
       </View>
     </View>
   )
 }
}

class rn_list extends Component {
 render() {
   return (
     <ItemList/>
   );
 }
}

AppRegistry.registerComponent('rn_list', () => rn_list);
``

The issue doesn't happen if in sample above to update line with arrays values to the following:

let items = this.state.longList ? ["Long11", "Long22", "Long23"] : ["Long11", "Long22"];

Nice to implement some automated tests to verify work results of UIManager::manageChildren