Add support for CASE_INSENSITIVE_ORDER in JS and common

#KT-18067

libraries/stdlib/js/src/kotlin/string.kt

@@ -105,4 +105,11 @@ public actual fun String.compareTo(other: String, ignoreCase: Boolean = false):
     } else {
         return compareTo(other)
     }
-}
+}
+
+
+private val STRING_CASE_INSENSITIVE_ORDER = Comparator<String> { a, b -> a.compareTo(b, ignoreCase = true) }
+
+@SinceKotlin("1.2")
+public actual val String.Companion.CASE_INSENSITIVE_ORDER: Comparator<String>
+    get() = STRING_CASE_INSENSITIVE_ORDER