add a smoke test

Author: ciscorn

packages/svelte/tests/runtime-browser/samples/typescript-class-and-interface/_config.js

@@ -0,0 +1,3 @@
+import { test } from '../../assert';
+
+export default test({});

packages/svelte/tests/runtime-browser/samples/typescript-class-and-interface/main.svelte

@@ -0,0 +1,5 @@
+<script lang="ts">
+  // TypeScript syntax should not cause compilation failure
+  interface MyInterface {}
+  class MyClass implements MyInterface {}
+</script>