Minor, add test on enum assignability to kotlin.Enum

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

@@ -0,0 +1,14 @@
+import java.lang.annotation.RetentionPolicy
+
+enum class E {
+    ENTRY
+}
+
+// Test resolve from source
+val a: Enum<E> = E.ENTRY
+
+// Test Java resolve
+val b: Enum<RetentionPolicy> = RetentionPolicy.RUNTIME
+
+// Test deserialized resolve
+val c: Enum<InlineOption> = InlineOption.ONLY_LOCAL_RETURN