pr-writer-impl lower level impl for js object printing

* remove pr-writer-impl dependence on lazy seq, MapEntry
  - use Array.map instead of map
  - reify IMapEntry instead of concrete MapEntry
* use primitive regex method

Author: swannodette

src/main/cljs/cljs/core.cljs

@@ -10529,9 +10529,15 @@ reduces them without incurring seq initialization"
         (do
           (-write writer "#js ")
           (print-map
-            (map (fn [k]
-                   (MapEntry. (cond-> k (some? (re-matches #"[A-Za-z_\*\+\?!\-'][\w\*\+\?!\-']*" k)) keyword) (unchecked-get obj k) nil))
-              (js-keys obj))
+            (.map
+              (js-keys obj)
+              (fn [k]
+                (reify
+                  IMapEntry
+                  (-key [_]
+                    (cond-> k (some? (.match k #"^[A-Za-z_\*\+\?!\-'][\w\*\+\?!\-']*$")) keyword))
+                  (-val [_]
+                    (unchecked-get obj k)))))
             pr-writer writer opts))
 
         (array? obj)