Kotlin: Add test case for missing enum constants

java/ql/test/kotlin/library-tests/enum/enumUser.kt

@@ -1 +1,3 @@
 fun usesEnum(e: Enum<*>) = e.ordinal.toString() + e.name
+
+enum class E { A, B, C }

java/ql/test/kotlin/library-tests/enum/test.expected

@@ -1,3 +1,5 @@
+enumConstants
+#select
 | addAll |
 | addRange |
 | allOf |

java/ql/test/kotlin/library-tests/enum/test.ql

@@ -3,3 +3,5 @@ import java
 from Method m
 where m.getDeclaringType().getName().matches("Enum%")
 select m.getName()
+
+query predicate enumConstants(EnumConstant ec) { ec.fromSource() }