Fabric: Add and subtract operations for RectangleEdges<T>

Summary:
We will use it soon for `EdgeInsets`

Changelog: [Internal] Fabric-specific internal change.

Reviewed By: sammy-SC

Differential Revision: D18444732

fbshipit-source-id: f03aa2a8889d426095a954d88f9cb6172c3e376e

Author: shergin

ReactCommon/fabric/graphics/Geometry.h

@@ -141,6 +141,26 @@ struct RectangleEdges {
   }
 };
 
+template <typename T>
+RectangleEdges<T> operator+(
+    RectangleEdges<T> const &lhs,
+    RectangleEdges<T> const &rhs) {
+  return RectangleEdges<T>{lhs.left + rhs.left,
+                           lhs.top + rhs.top,
+                           lhs.right + rhs.right,
+                           lhs.bottom + rhs.bottom};
+}
+
+template <typename T>
+RectangleEdges<T> operator-(
+    RectangleEdges<T> const &lhs,
+    RectangleEdges<T> const &rhs) {
+  return RectangleEdges<T>{lhs.left - rhs.left,
+                           lhs.top - rhs.top,
+                           lhs.right - rhs.right,
+                           lhs.bottom - rhs.bottom};
+}
+
 /*
  * Generic data structure describes some values associated with *corners*
  * of a rectangle.