Add reference assemblies and runtime targets support to dependency context builder.

src/Microsoft.DotNet.ProjectModel/Graph/LockFileRuntimeTarget.cs

@@ -0,0 +1,21 @@
+// Copyright (c) .NET Foundation and contributors. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+namespace Microsoft.DotNet.ProjectModel.Graph
+{
+    public class LockFileRuntimeTarget
+    {
+        public LockFileRuntimeTarget(string path, string runtime, string assetType)
+        {
+            Path = path;
+            Runtime = runtime;
+            AssetType = assetType;
+        }
+
+        public string Path { get; }
+
+        public string Runtime { get; }
+
+        public string AssetType { get; }
+    }
+}