5.0.0

Change

• 6108a76 Update @types/mdast
  migrate: update too
• 00c9c30 Change to require Node.js 16
  migrate: update too
• 72879f3 Change to use export map
  migrate: don’t use private APIs
• 0e5b32b Change to return undefined
  migrate: expect `undefined

Full Changelog: 4.1.1...5.0.0