Add --debug flag to the CLI dev command

[frandiox]

WHY are these changes introduced?

Related: #866 (comment)

To support the --debug flag that the Remix CLI already has.

WHAT is this pull request doing?

Opens a Node inspector when the --debug flag is provided, similar to what Remix CLI does.

HOW to test your changes?

1. Run h2 dev --debug in a template directory.
2. Open chrome://inspect and choose the only target that should appear.
3. Optionally add debugger; lines to server.ts or other parts of the code.
4. Open localhost:3000 in the browser and play with it.

Checklist

• I've read the Contributing Guidelines
• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've added a changeset if this PR contains user-facing or noteworthy changes
• I've added tests to cover my changes
• I've added or updated the documentation

[frehner]

I don't mind doing it this way, but I feel like it would be a better long-term solution if we could just pass any extra flags we get to the remix cli, and that way we're not reimplementing flags that already exist in remix.

Thoughts? @blittle

[frandiox]

We are not using the Remix CLI directly, but its internals.
Unfortunately, the usage of --debug in Remix CLI is in a very early point in their code that we can't reuse, that's why I'm just replicating that functionality here.
I agree that ideally we'd just reuse their whole CLI, but there are some limitations in that area (integration with MiniOxygen, custom logs, etc).

[frehner]

We are not using the Remix CLI directly, but its internals.

Ah, that's unfortunate. Thanks for the context.