[K/N] Use iterator in AbstractMutableList.indexOf/lastIndexOf

Instead of access by index. To avoid performance issues
when the subclass `get(index)` has non-constant time complexity.
It also aligns behavior with JVM.

libraries/stdlib/js/src/kotlin/collections/AbstractMutableList.kt

@@ -67,23 +67,9 @@ public actual abstract class AbstractMutableList<E> protected actual constructor
 
     actual override fun contains(element: E): Boolean = indexOf(element) >= 0
 
-    actual override fun indexOf(element: E): Int {
-        for (index in 0..lastIndex) {
-            if (get(index) == element) {
-                return index
-            }
-        }
-        return -1
-    }
+    actual override fun indexOf(element: E): Int = indexOfFirst { it == element }
 
-    actual override fun lastIndexOf(element: E): Int {
-        for (index in lastIndex downTo 0) {
-            if (get(index) == element) {
-                return index
-            }
-        }
-        return -1
-    }
+    actual override fun lastIndexOf(element: E): Int = indexOfLast { it == element }
 
     actual override fun listIterator(): MutableListIterator<E> = listIterator(0)
     actual override fun listIterator(index: Int): MutableListIterator<E> = ListIteratorImpl(index)