sum and sumBy supported

idea/testData/intentions/loopToCallChain/sum/indexUsed.kt

@@ -0,0 +1,10 @@
+// WITH_RUNTIME
+// INTENTION_TEXT: "Replace with 'mapIndexed{}.sum()'"
+// INTENTION_TEXT_2: "Replace with 'asSequence().mapIndexed{}.sum()'"
+fun foo(list: List<Int>): Int {
+    var s = 0
+    <caret>for ((index, item) in list.withIndex()) {
+        s += item * index
+    }
+    return s
+}