Replies without replied-to content in reply body

Some clients don't have the replied to message in body or format_body fields. So one has to rely on the event_id cited in m.relates_to->m.in_reply_to. Example of such an event is (I stripped out the id),

```
((:id . "ID")
(:sender . "@_discord_296842705454235650:t2bot.io")
(:content
(body . "sheesh u passed out at 4pm?")
(format . "org.matrix.custom.html")
(formatted_body . "sheesh u passed out at 4pm?")
(m\.relates_to
(m\.in_reply_to
(event_id . "$TluJm8weVHXI3gwsD-kSeI1HM3UOGIzqe8b-ybmdyb4")))
(msgtype . "m.text"))
(:origin-server-ts . 1648191029121)
(:type . "m.room.message")
(:state-key)
(:unsigned))
```

This is from the t2bot bridging a discord channel and a matrix room.

I can take a stab at implementing this on May.