TextInput: Fixed autoscroll to cursor on Android

Summary:
This feature was disabled for multiline textinputs in D3528202 ... seems without a good reason.
The broken autoscroll-to-cursor feature is terribly harmful and counter-intuitive in ALL cases.
I also add a contentSize tracking in the example app to make sure that it is unaffected by this change.

https://pxl.cl/9RHP

https://github.com/facebook/react-native/issues/12799
https://github.com/facebook/react-native/issues/15778

Special thanks to konradkierus!

Reviewed By: sahrens

Differential Revision: D6405985

fbshipit-source-id: 337a390a9db7b3528200ef66c4a079b87608294e

RNTester/js/TextInputExample.android.js

@@ -320,10 +320,14 @@ class AutogrowingTextInputExample extends React.Component<{}> {
       width: 100,
       multiline: true,
       text: '',
+      contentSize: {
+        width: 0,
+        height: 0,
+      },
     };
   }
 
-  componentDidReceiveProps(props) {
+  componentWillReceiveProps(props) {
     this.setState({
       multiline: props.multiline,
     });
@@ -351,10 +355,12 @@ class AutogrowingTextInputExample extends React.Component<{}> {
           multiline={this.state.multiline}
           style={[style, {width: this.state.width + '%'}]}
           onChangeText={(value) => this.setState({text: value})}
+          onContentSizeChange={(event) => this.setState({contentSize: event.nativeEvent.contentSize})}
           {...props}
         />
         <Text>Plain text value representation:</Text>
         <Text>{this.state.text}</Text>
+        <Text>Content Size: {JSON.stringify(this.state.contentSize)}</Text>
       </View>
     );
   }