Expose method to set custom baseline function

Summary:
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I was trying to typeset mathematical equations in react native. When typesetting fractions, baseline of the fraction must be aligned with the baseline of others. The baseline of fraction will vary based on size of numerator and denominator.

![image](https://user-images.githubusercontent.com/31202232/29577330-a22b45ee-8788-11e7-9cc5-04a72bcc1180.png)

 In yoga, we can set custom baseline function using `YogaNode.setBaselineFunction` method. If this method is exposed in `ReactShadowNode` class, it will be easy to create custom native UI modules which requires setting custom baseline.
Closes #15605

Differential Revision: D5686876

Pulled By: shergin

fbshipit-source-id: 34d797a7ea27d5c1b9f6b9c36e469cdca3883aec

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

@@ -22,6 +22,7 @@
 import com.facebook.yoga.YogaDirection;
 import com.facebook.yoga.YogaFlexDirection;
 import com.facebook.yoga.YogaJustify;
+import com.facebook.yoga.YogaBaselineFunction;
 import com.facebook.yoga.YogaMeasureFunction;
 import com.facebook.yoga.YogaNode;
 import com.facebook.yoga.YogaOverflow;
@@ -782,6 +783,10 @@ public void setShouldNotifyOnLayout(boolean shouldNotifyOnLayout) {
     mShouldNotifyOnLayout = shouldNotifyOnLayout;
   }
 
+  public void setBaselineFunction(YogaBaselineFunction baselineFunction) {
+    mYogaNode.setBaselineFunction(baselineFunction);
+  }
+
   public void setMeasureFunction(YogaMeasureFunction measureFunction) {
     if ((measureFunction == null ^ mYogaNode.isMeasureDefined()) &&
         getChildCount() != 0) {