JS backend: using native implementations in kotlin_lib.js for String.startsWith, String.endsWith and String.contains.

js/js.libraries/src/core/stringsCode.kt

@@ -25,21 +25,14 @@ public inline fun String.endsWith(ch: Char): Boolean {
     return if (s > 0) charAt(s - 1) == ch else false
 }
 
-public inline fun String.startsWith(text: String): Boolean {
-    val size = text.length
-    return if (size <= this.length) {
-        substring(0, size) == text
-    } else false
-}
+native
+fun String.startsWith(s:String):Boolean = noImpl
 
-public inline fun String.endsWith(text: String): Boolean {
-    val matchSize = text.length
-    val thisSize = this.length
-    return if (matchSize <= thisSize) {
-        substring(thisSize - matchSize, thisSize) == text
-    } else false
-}
+native
+fun String.endsWith(s:String):Boolean = noImpl
 
+native
+fun String.contains(s:String):Boolean = noImpl
 
 /**
  * Returns a copy of this string capitalised if it is not empty or already starting with an uppper case letter, otherwise returns this