Typeset Big-O complexities with Tex-style notation (#16090)
I've converted Big-Os that are visible in Haddock into TeX-notation. That way they look a bit nicer. Big-Os that aren't shown in Haddock (e.g. because they are in "Notes" blocks) stay untouched.
Please see #16090 (closed) for details.
Thanks in advance for reviewing! :)