Expose methods to set position Start|End

Summary:
As they're were not available yet.

Emil, I'm going to wait for your diffs to land before pushing this to
avoid disruptions on your side.

Differential Revision: D3669177

fbshipit-source-id: b06f382cb89546e817a2475298cf2cad17d95a2c

java/com/facebook/csslayout/CSSNodeAPI.java

@@ -68,6 +68,10 @@ public interface CSSNodeAPI<CSSNodeType extends CSSNodeAPI> {
   void setPositionLeft(float positionLeft);
   float getPositionRight();
   void setPositionRight(float positionRight);
+  float getPositionStart();
+  void setPositionStart(float positionStart);
+  float getPositionEnd();
+  void setPositionEnd(float positionEnd);
   float getStyleWidth();
   void setStyleWidth(float width);
   float getStyleHeight();