Simplify memory model between managed and unmanaged memory

Summary: Instead of having different lifetimes for java and c memory we can can tie them together and make them much easier to manage. This also leads to automatically pooling native memory if pooling java memory.

Differential Revision: D4051454

fbshipit-source-id: 8f5d010be520b3d1c981a7f85e5e6d95773ea6c1

csharp/Facebook.CSSLayout/Native.cs

@@ -37,6 +37,9 @@ namespace Facebook.CSSLayout
         [DllImport(DllName)]
         public static extern void CSSNodeFree(IntPtr cssNode);
 
+        [DllImport(DllName)]
+        public static extern void CSSNodeReset(IntPtr cssNode);
+
         [DllImport(DllName)]
         public static extern int CSSNodeGetInstanceCount();