Fix TextInput Spannable flags

Summary:
The TextInput spannables are being set wrong by Nodes. Consequently,
when you hit space after a word, anything you type is highlighted, though it
shouldn't be.

Differential Revision: D3507516

ReactAndroid/src/main/java/com/facebook/react/flat/RCTTextInput.java

@@ -169,6 +169,11 @@ public class RCTTextInput extends RCTVirtualText implements AndroidView, CSSNode
     return true;
   }
 
+  @Override
+  boolean isEditable() {
+    return true;
+  }
+
   @Override
   protected void performCollectText(SpannableStringBuilder builder) {
     if (mText != null) {