FB messenger supports it on desktop only. [0]

[0] https://news.ycombinator.com/item?id=13799800

(Sorry for the indirect sourcing)

Slack does: https://get.slack.help/hc/en-us/articles/204145658-Creating-...

Discord does: wrap your code in `` inline or ``` for a block.

Language highlighting can be supplied too:

  ```cpp
  /* some C++ code here */
  ```

Telegram does:

for one-liners: use `your one liner`

for multiline snippets: ``` multiline snippet ```

note there is no code highlight

Skype does: Start your message with `!! ` (without the back ticks).