refactor: move to tsdown

[lishaduck]

As per #1439 (comment).

Passes attw, publint.

We can probably drop some of the babel deps now, but I don't know enough about mocha & babel-node to know what.

[lishaduck]

Anything else you'd like changed?

[brettz9]

No, just need some time to review.

[brettz9]

While the results are better on attw, there are these resolution errors still:

[lishaduck]

While the results are better on attw, there are these resolution errors still:

Those are for the node10 resolution mode, which has been discouraged for years, is no longer the default in TS 5.9, and will be removed in TS 7.
I'll fix the main entrypoint, but fixing the rest requires a bunch of nasty hacks just to support projects that are using ~unsupported settings.

[brettz9]

I undid the Node10 fixes and removed the Babel dependencies we can remove.

If there is no CLI for unplugin-unused, and there is no script, can we remove that too now?

[lishaduck]

unplugin-unused is an (optional) dependency of tsdown. It checks that the dist is consistent with what gets bundled.

[github-actions]

🎉 This PR is included in version 52.0.3 🎉

The release is available on:

• GitHub release
• npm package (@latest dist-tag)

Your semantic-release bot 📦🚀

[brettz9]

Unfortunately had to revert this due to #1443.