JS stdlib: implement String.compareTo with ignoreCase

#KT-18067 Fixed

libraries/stdlib/common/src/kotlin/TextH.kt

@@ -290,6 +290,11 @@ expect fun Int.toString(radix: Int): String
 @SinceKotlin("1.2")
 expect fun Long.toString(radix: Int): String
 
+/**
+ * Compares two strings lexicographically, optionally ignoring case differences.
+ */
+expect fun String.compareTo(other: String, ignoreCase: Boolean = false): Int
+
 @PublishedApi
 internal expect fun checkRadix(radix: Int): Int