Extend ReactShadowNode API to expose flex props

Summary:
This diff extends the ReactShadowNode API to expose flex props, this is going to be used by some components that require access to it

changeLog: [Android][Added] Exposed getFlex method as part of ReactShadowNode API

Reviewed By: JoshuaGross

Differential Revision: D21554663

fbshipit-source-id: 26c9a3fe5f72a84120b16b553ab08231817c0efa

Author: mdvacca

ReactAndroid/src/main/java/com/facebook/react/uimanager/ReactShadowNode.java

@@ -288,6 +288,8 @@ public interface ReactShadowNode<T extends ReactShadowNode> {
 
   YogaValue getStyleHeight();
 
+  float getFlex();
+
   void setStyleHeight(float heightPx);
 
   void setStyleHeightPercent(float percent);

ReactAndroid/src/main/java/com/facebook/react/uimanager/ReactShadowNodeImpl.java

@@ -779,6 +779,11 @@ public void setStyleMaxHeightPercent(float percent) {
     mYogaNode.setMaxHeightPercent(percent);
   }
 
+  @Override
+  public float getFlex() {
+    return mYogaNode.getFlex();
+  }
+
   @Override
   public void setFlex(float flex) {
     mYogaNode.setFlex(flex);