Add setNativeProps

Summary:
Curently FlatList does not implement setting native props directly like the old ListView did. This pr introduce the `setNativeProps` function which delegates to MetroListView or VirtualizedList. Thos don't have `setNativeProps` handling either, so, I delegated further to the respective ListView and Scroll components, which do have handling for it, thus, allowing to set the native props through FlatList.

Create a project with a FlatList and change a native property using `setNativeProps`:

```javascript
  componentDidMount() {
        setInterval(() => {
            this.list.setNativeProps({ style: {backgroundColor:"white"} })
        }, 1000)
    }

  render() {
    return (
      <View style={styles.container}>
        <FlatList ref={component => this.list = component}
                  style={{backgroundColor:"black"}}
                  data={[{key: 'a'}, {key: 'b'}]}
                  renderItem={({item}) => <Text>{item.key}</Text>} />
      </View>
    )
  }
```

Fixes #13501
Closes https://github.com/facebook/react-native/pull/13529

Differential Revision: D5283593

Pulled By: sahrens

fbshipit-source-id: 8f96f88e286042d82452fef924689b5a8a783987

Libraries/Lists/FlatList.js

@@ -388,6 +388,12 @@ class FlatList<ItemT>
     }
   }
 
+  setNativeProps(props: Object) {
+    if (this._listRef) {
+      this._listRef.setNativeProps(props);
+    }
+  }
+
   componentWillMount() {
     this._checkProps(this.props);
   }

Libraries/Lists/MetroListView.js

@@ -95,6 +95,11 @@ class MetroListView extends React.Component {
   getListRef() {
     return this._listRef;
   }
+  setNativeProps(props: Object) {
+    if (this._listRef) {
+      this._listRef.setNativeProps(props);
+    }
+  }
   static defaultProps: DefaultProps = {
     keyExtractor: (item, index) => item.key || String(index),
     renderScrollComponent: (props: Props) => {

Libraries/Lists/VirtualizedList.js

@@ -313,6 +313,12 @@ class VirtualizedList extends React.PureComponent<OptionalProps, Props, State> {
     }
   }
 
+  setNativeProps(props: Object) {
+    if (this._scrollRef) {
+      this._scrollRef.setNativeProps(props);
+    }
+  }
+
   static defaultProps = {
     disableVirtualization: false,
     horizontal: false,