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");
  },
};
```

1 files changed, 1 insertions, 0 deletions

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/