Use appropriate coding system when unzipping jars

[pdbrown]

in cider-find-file. This prevents CRLF encoded files from appearing with ^M
characters at the end of each line, which, in turn, avoids confusing
clojure-find-ns and breaking cider-find-var.
clojure-find-ns uses Emacs' (thing-at-point 'symbol) as part of identifying
a file's namespace, and when a file isn't decoded properly, namespaces can be
reported as my.lib^M which cider-find-var won't know what to do with.

---

Hey again! I came across https://github.com/clojure-emacs/cider/discussions/2957 today, where @expez mentions cider-find-var is broken in jars. I do this all the time and it works fine, so I looked into the repro a little and found that cider-find-var was getting confused in cljfx.api, as extracted from its jar, because it has windows line endings.

The nrepl message trace:

(-->
  id         "14"
  op         "info"
  session    "5cf7e082-fe85-448e-bc8f-9bb99e038211"
  time-stamp "2021-04-15 14:33:35.951811315"

  ns         #("cljfx.api^M" 0 10 (fontified nil))
;;                        ^--- broken!

  sym        "event-handler/dispatch-effect"
)
(<--
  id         "14"
  session    "5cf7e082-fe85-448e-bc8f-9bb99e038211"
  time-stamp "2021-04-15 14:33:35.954095391"
  status     ("done" "no-info")
)

The ns value is obtained from clojure-find-ns via (thing-at-point 'symbol), which will include the ^M if it's there.
While we could wrap a (string-trim-right ...) around the ns name somewhere, that shouldn't really be necessary, and clojure-mode uses thing-at-point in several other ways so this might not be the only broken thing. The ^Ms are also a bit of an eyesore, so I think attempting to get rid of them is the way to go. People might still be broken by files with mixed encoding though.

---

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[bbatsov]

The fix looks good. Just mention it in the changelog and we're good to go.

[bbatsov]

Thanks!