sum and sumBy supported

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

@@ -0,0 +1,14 @@
+// WITH_RUNTIME
+// IS_APPLICABLE: false
+// IS_APPLICABLE_2: false
+class C
+
+operator fun C.plus(other: C): C = TODO()
+
+fun foo(list: List<C>): C {
+    var s = C()
+    <caret>for (item in list) {
+        s += item
+    }
+    return s
+}