feat: Add `deno serve` subcommand (#23511)

By default, `deno serve` will assign port 8000 (like `Deno.serve`).
Users may choose a different port using `--port`.

`deno serve /tmp/file.ts`

`server.ts`:
```ts
export default {
  fetch(req) {
    return new Response("hello world!\n");
  },
};
```

3 files changed, 24 insertions, 0 deletions

diff --git a/tests/specs/serve/basic/__test__.jsonc b/tests/specs/serve/basic/__test__.jsonc
new file mode 100644
index 000000000..9a37d60ff
--- /dev/null
+++ b/tests/specs/serve/basic/__test__.jsonc
@@ -0,0 +1,5 @@
+{
+  "args": "serve --port 12345 main.ts",
+  "output": "main.out",
+  "tempDir": true
+}
diff --git a/tests/specs/serve/basic/main.out b/tests/specs/serve/basic/main.out
new file mode 100644
index 000000000..e79d76af5
--- /dev/null
+++ b/tests/specs/serve/basic/main.out
@@ -0,0 +1 @@
+deno serve: Listening on http://localhost:12345/
diff --git a/tests/specs/serve/basic/main.ts b/tests/specs/serve/basic/main.ts
new file mode 100644
index 000000000..9e299ab21
--- /dev/null
+++ b/tests/specs/serve/basic/main.ts
@@ -0,0 +1,18 @@
+(async () => {
+  for (let i = 0; i < 1000; i++) {
+    try {
+      const resp = await fetch("http://localhost:12345/");
+      Deno.exit(0);
+    } catch {
+      await new Promise((r) => setTimeout(r, 10));
+    }
+  }
+
+  Deno.exit(2);
+})();
+
+export default {
+  fetch(req) {
+    return new Response("Hello world!");
+  },
+};