Support "Lift return out of when" for exhaustive when without else

So #KT-18852 Fixed

idea/testData/inspectionsLocal/liftOut/whenToAssignment/whenHasMissingCase.kt

@@ -0,0 +1,16 @@
+// PROBLEM: none
+
+enum class TestEnum{
+    A, B, C
+}
+
+fun test(e: TestEnum): Int {
+    var res: Int = 0
+
+    <caret>when (e) {
+        TestEnum.A -> res = 1
+        TestEnum.B -> res = 2
+    }
+
+    return res
+}