feat(timeline): support MSC4293 redact-on-ban/kick

[turt2live]

Disclaimer: I don't know enough Rust to meaningfully make this work, so trying to get the PR 90% there instead.

Known issues:

• [ ] ev.content["org.matrix.msc4293.redact_events"] isn't how any of this works
• [ ] The room_info redaction isn't applied
• [ ] There are no tests

If it's easier to throw this all away and try again, please feel free.