Include resource links in the tree navigation

[elycheea]

Detailed description

Describe in detail the issue you’re having.

In the Gatsby theme, the resource links are separate from the left nav and left nav tree. When using the left nav, you are able to tab to these ResourceLinks, but using the tree nav, you are not able to reach the resource links via keyboard.

What did you expect to happen? What happened instead? What would you like to see changed?

In both scenarios, the navigation to these links should follow the left nav links. (e.g. when tabbing from the left nav, these are the logical to be next in the tab order).

What browser are you working in?

Steps to reproduce the issue

1. Step one
2. Step two
3. Step three
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Additional information

• Screenshots or code
• Notes