mention REPL IOContext in pretty-printing docs (#53926)
Fix omission in pretty-printing docs mentioned here:
https://github.com/JuliaLang/julia/issues/53678#issuecomment-2033053880
(I think these docs were written before `IOContext` existed?)
Also fixes a corresponding place in the REPL docs, which mentioned the
`IOContext` but omitted `display`. Closes #53678
