feat: add http2.dart

http2.dart

@@ -0,0 +1,17 @@
+const listener = Deno.listenTls({
+  port: 443,
+  certFile: "./cert.pem",
+  keyFile: "./key.pem",
+  alpnProtocols: ["h2", "http/1.1"],
+});
+
+for await (const conn of listener) {
+  handleConn(conn);
+}
+
+async function handleConn(conn: Deno.Conn) {
+  const httpConn = Deno.serveHttp(conn);
+  for await (const { request, respondWith } of httpConn) {
+    respondWith(new Response(`Responding to ${request.url}`));
+  }
+}