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

Also includes minor test fix, related to KT-14900

idea/testData/inspectionsLocal/liftOut/ifToAssignment/simpleIfWithAugmentedAssignment.kt

@@ -0,0 +1,7 @@
+fun test(n: Int): String {
+    var res: String = "!"
+
+    <caret>if (n == 1) res += "one" else res += "two"
+
+    return res
+}