Prohibit extending kotlin.Enum directly

#KT-7773 Fixed

compiler/testData/diagnostics/tests/enum/extendingEnumDirectly.kt

@@ -0,0 +1,9 @@
+class Test1 : <!CLASS_CANNOT_BE_EXTENDED_DIRECTLY!>Enum<Test1><!>("", 0)
+
+class Outer {
+    class Test2 : <!CLASS_CANNOT_BE_EXTENDED_DIRECTLY!>Enum<Test2><!>("", 0)
+}
+
+fun outer() {
+    class Test3 : <!CLASS_CANNOT_BE_EXTENDED_DIRECTLY!>Enum<Test3><!>("", 0)
+}