Introduce `AccessibleLabel` component. (#24308)

See release notes for rationale and usage.

Fixes #17644, #20524

(It may not be a 100% fix, but it's good enough to close the ticket I
think.)

## Testing

- Manual testing with VoiceOver on MacOS (note that VoiceOver /
AccessKit does not work well without `desktop_app` being set, but this
causes other issues)

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Co-authored-by: Richard Braakman <rebraakman@gmail.com>