Kotlin: Add test case for unused extension parameters

Author: tamasvajk

java/ql/test/kotlin/query-tests/UselessParameter/Test.kt

@@ -9,3 +9,13 @@ class B : A<B, Int> {
 }
 
 fun fn(a: Int = 10) {}
+
+class C {
+    companion object {}
+}
+
+object O {}
+
+fun C.fn() {}
+fun C.Companion.fn() {}
+fun O.fn() {}

java/ql/test/kotlin/query-tests/UselessParameter/UselessParameter.expected

@@ -1 +1,4 @@
 | Test.kt:11:8:11:18 | a | The parameter 'a' is never used. |
+| Test.kt:19:5:19:5 | <this> | The parameter '<this>' is never used. |
+| Test.kt:20:5:20:15 | <this> | The parameter '<this>' is never used. |
+| Test.kt:21:5:21:5 | <this> | The parameter '<this>' is never used. |