JS stdlib: implement String.compareTo with ignoreCase

#KT-18067 Fixed

libraries/stdlib/jvm/src/kotlin/text/StringsJVM.kt

@@ -317,7 +317,7 @@ public inline fun String.codePointCount(beginIndex: Int, endIndex: Int): Int =
 /**
  * Compares two strings lexicographically, optionally ignoring case differences.
  */
-public fun String.compareTo(other: String, ignoreCase: Boolean = false): Int {
+public actual fun String.compareTo(other: String, ignoreCase: Boolean): Int {
     if (ignoreCase)
         return (this as java.lang.String).compareToIgnoreCase(other)
     else