CLJS-1547: Wrong output encoding when compile with goog.LOCALE

Closure Compiler uses ASCII by default because of legacy reasons.
Non-ASCII characters are escaped.
It may lead to larger builds when using i18n facilities.

Also, when using goog.i18n with custom goog.LOCALE option,
REPL users can see formatted dates in legacy encodings
of their languages (for example, CP1252 for goog.LOCALE="ru").

This patch provides UTF-8 encoding by default.
Possible options are:
 * US-ASCII (current default)
 * ISO-8859-1
 * UTF-8 (proposed default)
 * UTF-16BE
 * UTF-16LE
 * UTF-16
(https://docs.oracle.com/javase/8/docs/api/java/nio/charset/Charset.html)

Author: S. Zharinov

src/main/clojure/cljs/closure.clj

@@ -211,6 +211,9 @@
     (. compiler-options
       (setExtraAnnotationNames (map name (:closure-extra-annotations opts)))))
 
+  (. compiler-options
+     (setOutputCharset (:closure-output-charset opts "UTF-8")))
+
   compiler-options)
 
 (defn ^CompilerOptions make-options