#2628 - CSS hints insert rather than replace

Straight forward, remove the end parameter to replaceRange so it inserts instead. Also minor refactor to the `keepHints` return value, causing a new hint list to appear only after `:` and not `;` as noted in #2627. I'd vote to keep that one open as I agree with @njx that this is a pretty narrow 'fix' and a more general solution would be nicer for that issue.