cider-repl-require-repl-utils loads cljs repl utils

[rpkarlsson]

Part of the solution for #2647, loading cljs repl utils in cljs buffers.

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[rpkarlsson]

Still looking at:

Maybe we should rename this to cider-repl-init-code-clj and add some matching cljs counterpart (or make it an alist/plist) as well, so there's some init code that we'd run in ClojureScript REPLs after they are upgraded as well.
#2647 (comment)

But still trying to figure out how to run code once upgraded to a cljs repl. In the meantime I thought I'd make a PR of the first part.

[bbatsov]

Thanks for tackling this!