Add explicit dependency on @types/unist

[GuiltyDolphin]

Initial checklist

• I read the support docs
• I read the contributing guide
• I agree to follow the code of conduct
• I searched issues and couldn’t find anything (or linked relevant results below)
• If applicable, I’ve added docs and tests

Description of changes

This PR adds the latest version of @types/unist an explicit dependency (as we import from it directly).

Edit: I notice in the description that dependency on @types/unist is suggested for projects using typescript - is there a particular downside to depending on it directly here?

[GuiltyDolphin]

cc @wooorm @remcohaszing @ChristianMurphy

Should I bump unified's (patch?) version number too, so the change in typing doesn't affect packages depending on the old system?

[GuiltyDolphin]

Btw @ChristianMurphy @wooorm I'm working through the main unified packages to update @types/unist to the latest version. Because it is (technically) a breaking change, updating forces us to make sure we aren't expecting types in the old format, and for going forwards.

I've done a few repos (for the most part, the code doesn't need changing, just the dependencies), but I want to check with you both that I'm doing the correct thing before I go ahead with the others.

[ChristianMurphy]

Btw @ChristianMurphy @wooorm I'm working through the main unified packages to update @types/unist to the latest version. Because it is (technically) a breaking change, updating forces us to make sure we aren't expecting types in the old format, and for going forwards.

I've done a few repos (for the most part, the code doesn't need changing, just the dependencies), but I want to check with you both that I'm doing the correct thing before I go ahead with the others.

Thanks @GuiltyDolphin!
In general it is worth checking, looking for breaking changes.
We try to keep version ranges wide, for example ^2.0.0 rather than ^2.1.3 for example.
Which means not many repos will need their package.json updated, but a few may need their test suite or typings adjusted.

[GuiltyDolphin]

Alright! I'll keep checking through then, but without updating version numbers and just make sure that typings are okay for the latest version of @types/unist. It looks like we're mostly okay though, not too many packages are making assumptions about extra keys on Node. 😄