[Fix #3834] Change cider-ns-refresh to use Clojure REPL whenever one exists

[wilbrt]

Change cider-ns-refresh to use a Clojure REPL whenever one exists, by wrapping the function body in a with-current-buffer with the clj-repl connection if it exists. If not, throw a no-repls-user-error. Fixes #3834.

Not sure if this is a reasonable way to handle this, so all critiques and comments are more than welcome, thanks!

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Thanks!

If you're just starting out to hack on CIDER you might find this section of its
manual extremely useful.

[bbatsov]

Hmm, seems to me something's wrong with cider-map-repls, as I see it's invoked with :clj in this context which should be enough if things were working properly. (basically it filters out the non-Clojure connections)

[wilbrt]

There doesn't seem to be anything wrong with cider-map-repls. It's just that the lines
(cider-ensure-op-supported "refresh") (cider-ensure-op-supported "cider.clj-reload/reload") (cider-ns-refresh--save-modified-buffers) throw when the current buffers cider-current-repl does not give a Clojure repl.

I thought about extending the cider-ensure-op-supported-function to take an optional parameter for the repl type we want to use but figured it would change existing functionality too much for this kind of change.