Introduce "Unused unary operator" inspection

#KT-12073 Fixed

idea/testData/inspectionsLocal/unusedUnaryOperator/basic2.kt.after

@@ -0,0 +1,6 @@
+// "Remove unused unary operator" "true"
+fun test(foo: Int?): Int {
+    val a = 1 + 2
+    3
+    return a
+}