Update ObjectPool reference assemblies

\n\nCommit migrated from f13113c06b

src/ObjectPool/ref/Microsoft.Extensions.ObjectPool.netstandard2.0.cs

@@ -38,6 +38,10 @@ namespace Microsoft.Extensions.ObjectPool
         public override T Get() { throw null; }
         public override void Return(T obj) { }
     }
+    public static partial class ObjectPool
+    {
+        public static Microsoft.Extensions.ObjectPool.ObjectPool<T> Create<T>(Microsoft.Extensions.ObjectPool.IPooledObjectPolicy<T> policy = null) where T : class, new() { throw null; }
+    }
     public abstract partial class ObjectPoolProvider
     {
         protected ObjectPoolProvider() { }