Stabilize EnumEntries stdlib signature

* Also, mention implementation details of EnumEntries to enable safe uses of a 'EnumEntries' as a set
* Fix testdata for opt-in marker in enum entries

^KT-58548 fixed

Merge-request: KT-MR-10037
Merged-by: Vsevolod Tolstopyatov <qwwdfsad@gmail.com>

libraries/stdlib/api/js/kotlin.enums.kt

@@ -1,4 +1,4 @@
-@kotlin.ExperimentalStdlibApi
-@kotlin.SinceKotlin(version = "1.8")
+@kotlin.SinceKotlin(version = "1.9")
+@kotlin.WasExperimental(markerClass = {kotlin.ExperimentalStdlibApi::class})
 public sealed interface EnumEntries<E : kotlin.Enum<E>> : kotlin.collections.List<E> {
-}
+}