Provide MutableList.fill for JS, annotate new API with @SinceKotlin

#KT-8823 #KT-9010

js/js.libraries/src/core/collections.kt

@@ -79,6 +79,18 @@ public fun <T> setOf(element: T): Set<T> = hashSetOf(element)
  */
 public fun <K, V> mapOf(pair: Pair<K, V>): Map<K, V> = hashMapOf(pair)
 
+/**
+ * Fills the list with the provided [value].
+ *
+ * Each element in the list gets replaced with the [value].
+ */
+@SinceKotlin("1.2")
+public fun <T> MutableList<T>.fill(value: T) {
+    for (index in 0..lastIndex) {
+        this[index] = value
+    }
+}
+
 /**
  * Sorts elements in the list in-place according to their natural sort order.
  */