The bulk of this updates transcripts to put spaces around the language
name in code blocks. E.g.,
```` markdown
```ucm:hide
````
becomes
```` markdown
``` ucm :hide
````
This corresponds to
https://share.unison-lang.org/@unison/website/contributions/11, which
updates the docs in the same way.
This is effectively a fix for #5214, but that issue also has good recommendations for future changes to info strings, so
I don’t know that it should be closed.
