add React hook for scrolling to location anchor

Created by: sqs

This logic was previously implemented in a couple places separately and in an incomplete manner. Now there is a React hook that is well documented and comprehensive.

Test plan:

1. Go to http://localhost:3080/github.com/auth0/express-jwt/-/blob/README.md#revoked-tokens and ensure the browser scrolls down to the "Revoked tokens" section header automatically (even though that README's file content is loaded asynchronously).
2. Click on other section headers # links on that same document and ensure those are scrolled to.