start to implements async linq

src/UniTask.NetCore/IAsyncEnumerable.cs

@@ -0,0 +1,20 @@
+using System.Threading;
+
+namespace Cysharp.Threading.Tasks
+{
+    public interface IUniTaskAsyncEnumerable<out T>
+    {
+        IUniTaskAsyncEnumerator<T> GetAsyncEnumerator(CancellationToken cancellationToken = default);
+    }
+
+    public interface IUniTaskAsyncEnumerator<out T> : IUniTaskAsyncDisposable
+    {
+        T Current { get; }
+        UniTask<bool> MoveNextAsync();
+    }
+
+    public interface IUniTaskAsyncDisposable
+    {
+        UniTask DisposeAsync();
+    }
+}