Migrate sentry-replay into sentry-javascript #6257

We want to migrate https://github.com/getsentry/sentry-replay into this monorepo, as packages/replay.

• Ensure we keep Git branch history: https://blog.brunogarcia.com/2020/09/move-repositories-on-github-without.html
  • Ensure to run this on main of a fresh clone of the repo (doesn't work properly otherwise)
• Merge into monorepo - see e.g. https://blog.jdriven.com/2021/04/how-to-merge-multiple-git-repositories/
  • Create branch monorepo-merge off sentry-replay master
  • Move all files there into a packages/replay folder using git mv -k * packages/sentry-replay (make sure target dir exists)
  • Delete unneeded root-level files (e.g. .gitignore, ...) - make sure nothing important is lost there
  • Merge the monorepo-merge branch from sentry-replay into sentry-javascript, like this:

  cd ../MonoRepo (1)
  git remote add -f RepoA ../RepoA (2)
  git merge -m "Integrating RepoA" RepoA/prepare_monorepo --allow-unrelated-histories (3)
  git remote rm RepoA (4)
  

• Ensure existing tests run
• Ensure package is excluded from publishing etc.