[Monorepo] PR "move" and wrapping up

[pkra]

To wrap up the monorepo move, please complete the following:

• [x] review PRs (see link list below)
  • [x] close PRs that were "moved" correctly
  • [x] handle PRs from forks (which could not be "moved" the same way)
  • either alert authors to make new PRs to on the ARIA repository and close the PR
  • or (to maintain a useful diff) create a branch (e.g., "old_main") and change those PRs to target that branch
• [x] merge "closing" PR #237

PR list

• [x] #183 => https://github.com/w3c/aria/pull/2210
• [x] #229 => https://github.com/w3c/aria/pull/2209
• [x] #235 => https://github.com/w3c/aria/pull/2208
• [x] #236 => https://github.com/w3c/aria/pull/2207
• [x] #90 => TBD (on fork)