A small follow-up to #7221. This changes the `catch` block from a block
to a closure, so that it can access the error returned from the `try`
block. This helps with a common scenario: "the `try` block failed, and I
want to log why it failed."
### Example
![image](https://user-images.githubusercontent.com/26268125/203841966-f1f8f102-fd73-41e6-83bc-bf69ed436fa8.png)
### Future Work
Nu's closure syntax is a little awkward here; it might be nicer to allow
something like `catch err { print $err }`. We discussed this on Discord
and it will require special parser code similar to what's already done
for `for`.
I'm not feeling confident enough in my parser knowledge to make that
change; I will spend some more time looking at the `for` code but I
doubt I will be able to implement anything in the next few days.
Volunteers welcome.