Do not call Enum.values() on each call to decodeEnumValue for explicitly-serializable enums

[qwwdfsad]

Steps to reproduce:

@Serializable
enum class AnnotatedEnum {
    E1,
    E2
}

Its serializer.deserialize code contains the following sequence: AnnotatedEnum.values()[decoder.decodeEnum($$serialDesc)]; It triggers an allocation of values array on each call.

The desired behaviour is to pre-cache this array in serializer's state

[shanshin]

Fixed via #1851