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

Also includes minor test fix, related to KT-14900

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

@@ -0,0 +1,12 @@
+// PROBLEM: none
+fun test(s: String): Int {
+    var n: Int = 1;
+
+    <caret>if (s.equals("add")) {
+        n += 1
+    } else {
+        n -= 1
+    }
+
+    return n
+}