[stdlib] Explicit visibility and return types: JS

Stepping test line number changes are due to changes in coroutineInternalJS.kt

libraries/stdlib/js/builtins/String.kt

@@ -12,7 +12,7 @@ package kotlin
  * implemented as instances of this class.
  */
 public class String : Comparable<String>, CharSequence {
-    companion object {}
+    public companion object {}
     
     /**
      * Returns a string obtained by concatenating this string with the string representation of the given [other] object.