TextInput: support text value+child Text nodes

Summary:
Fix and simplify `AndroidTextInputShadowNode::getAttributedString` so that it (1) works, and (2) is aligned with the equivalents in the old Java code.

The issue is that we weren't picking up `text` attributes since we're only traversing children and not the TextInput node itself. If a `text` attribute is present it needs to be treated as its own Text node.

Changelog: [Internal]

Reviewed By: mdvacca

Differential Revision: D18739830

fbshipit-source-id: 4b3bc81dbe8c241c2e06fe5be1f9b50e49132890

ReactAndroid/src/main/java/com/facebook/react/views/textinput/ReactTextInputManager.java

@@ -212,6 +212,7 @@ public class ReactTextInputManager extends BaseViewManager<ReactEditText, Layout
         break;
       case "setTextAndSelection":
         int mostRecentEventCount = args.getInt(0);
+        reactEditText.setMostRecentEventCount(mostRecentEventCount);
 
         if (mostRecentEventCount != UNSET) {
           String text = args.getString(1);