Use NavList component

[colebemis]

I replaced Doctocat's custom navigation components with the new NavList component.

Before

After

---

Breaking change

Items in nav.yml that contain children no longer render as links, meaning the url property will be ignored.

# nav.yml
– title: Components
- url: /components
  children:
   — title: Avatar
     url: /Avatar

Related https://github.com/github/primer/issues/395

[changeset-bot]

🦋 Changeset detected

Latest commit: 3a9de25

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@primer/gatsby-theme-doctocat	Major

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[colebemis]

Tests are failing because JSDOM doesn't mock ResizeObserver.

• Copy the ResizeObserver mock from primer/react: https://github.com/primer/react/blob/main/src/utils/test-helpers.tsx

[colebemis]

@siddharthkp verbally approved this in a 1:1 ✅