add license header

Author: e111077

packages/lit-dev-content/src/global/lit-hydrate-support.ts

@@ -1,3 +1,9 @@
+/**
+ * @license
+ * Copyright 2022 Google LLC
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
 // This file is needed for rollup bundling order despite it never being loaded
 // in Production. Loading this file directly in prod in default.html would cause
 // an unnecessary second request to lit.js