Convert "lift return / assignment" intentions into a single inspection

Also includes minor test fix, related to KT-14900

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

@@ -0,0 +1,10 @@
+fun test(n: Int): String {
+    var res: String
+
+    <caret>when (n) {
+        1 -> res = "one"
+        else -> res = "two"
+    }
+
+    return res
+}