Added blurOnSubmit support to multine TextInput (aka RCTTextView)

Summary:
public

Setting `blurOnSubmit=true` on a multiline `<TextInput>` now causes it to behave like a single-line input with respect to the return key:

With the default value of `false`, pressing return will enter a newline character into the field. If you set the value to `true`, pressing return will now blur the field and trigger the onSubmitEditing event. The newline character will *not* be added to the text.

(See associated github task for dicussion: https://github.com/facebook/react-native/pull/2149)

Reviewed By: javache

Differential Revision: D2710448

fb-gh-sync-id: c9706ae11f8b399932d3400ceb4c7558e455570d

Examples/UIExplorer/TextInputExample.ios.js

@@ -548,6 +548,23 @@ exports.examples = [
     title: 'Blur on submit',
     render: function(): ReactElement { return <BlurOnSubmitExample />; },
   },
+  {
+    title: 'Multiline blur on submit',
+    render: function() {
+      return (
+        <View>
+          <TextInput
+            style={styles.multiline}
+            placeholder='blurOnSubmit = true'
+            returnKeyType='next'
+            blurOnSubmit={true}
+            multiline={true}
+            onSubmitEditing={event => alert(event.nativeEvent.text)}
+          />
+        </View>
+      );
+    }
+  },
   {
     title: 'Multiline',
     render: function() {