New J2K: calculate for loop variable nullability

nj2k/testData/nullabilityAnalysis/loops.kt

@@ -0,0 +1,16 @@
+fun bar(map: HashMap<String, Int>, list1: List<Int>, list2: List<String>) {
+    for (entry: MutableMap.MutableEntry<String, Int> in map.entries) {
+        val value: Int = entry.value
+        if (entry.key == null) {
+            println(value + 1)
+        }
+    }
+
+    for (i: Int in list1) {
+        i + 1
+    }
+
+    for (i: String in list2) {
+        i == null
+    }
+}

nj2k/testData/nullabilityAnalysis/loops.kt.after

@@ -0,0 +1,16 @@
+fun bar(map: HashMap<String?, Int>, list1: List<Int>, list2: List<String?>) {
+    for (entry: MutableMap.MutableEntry<String?, Int> in map.entries) {
+        val value: Int = entry.value
+        if (entry.key == null) {
+            println(value + 1)
+        }
+    }
+
+    for (i: Int in list1) {
+        i + 1
+    }
+
+    for (i: String? in list2) {
+        i == null
+    }
+}