Introduce CSSLayoutSetLogger to pass the print result to C# side

Summary:
- CSSLayoutSetLogger
  - Problem: Unity or other logging system can't use printf output
  - Solution: Add CSSLogger to pass CSSNodePrint result to UnityEngine.Debug.Log or other logging system via CSSLogger function for debugging purpose

Reviewed By: emilsjolander

Differential Revision: D4027044

fbshipit-source-id: 90e2e449260888770f71fa7ea790ca9764d91c44

csharp/Facebook.CSSLayout/Native.cs

@@ -20,6 +20,9 @@ namespace Facebook.CSSLayout
         private const string DllName = "CSSLayout";
 #endif
 
+        [DllImport(DllName)]
+        public static extern void CSSInteropSetLogger(CSSLogger.Func func);
+
         [DllImport(DllName)]
         public static extern void CSSAssertSetFailFunc(CSSAssert.FailFunc func);
 
@@ -81,12 +84,6 @@ namespace Facebook.CSSLayout
         [DllImport(DllName)]
         public static extern CSSMeasureFunc CSSNodeGetMeasureFunc(IntPtr node);
 
-        [DllImport(DllName)]
-        public static extern void CSSNodeSetPrintFunc(IntPtr node, CSSPrintFunc printFunc);
-
-        [DllImport(DllName)]
-        public static extern CSSPrintFunc CSSNodeGePrintFunc(IntPtr node);
-
         [DllImport(DllName)]
         public static extern void CSSNodeSetIsTextnode(IntPtr node, [MarshalAs(UnmanagedType.I1)] bool isTextNode);