3.0.0

Change

• 02f3792 Update @types/mdast, mdast utilities
  migrate: update too
• 18e8b87 Change to require Node 16
  migrate: update too
• d595da7 Change to use exports
  migrate: don’t use private APIs
• a0f2c46 Change to return undefined, not null
  migrate: expect undefined
• 82c674d Remove support for MDX 1 comments
  migrate: use MDX 2

Full Changelog: 2.1.2...3.0.0