Transform ' to "

[lionel-]

This should possibly be one of the few options in the formatter. The tidyverse style guide recommends " but I think it's legitimate to use ' in codebases or projects that also use Python of JS/TS where ' is the norm.

[lionel-]

A similar issue is = vs <-. Multi-lingual codebases might prefer = to make context switches easier. Either we deal with this through linting or we add an air.toml option.

I think I'd like the formatter to normalise these though. This makes it easier to copy paste code from repos that have different conventions.