[9] RFR (M): 8050884: Intrinsify ValueConversions.identity() functions

[Vladimir Ivanov]

Thanks for review, Paul.

> Looks good.
>
> Same question as in previous email on @Stable for MethodHandles.IDENTITY_MHS.
>
> FWIW for MethodHandles.IDENTITY_MHS the Wrapper.ordinal() is used as an index rather than using an EnumMap.
Yes, caching logic is inconsistent across java.lang.invoke. I'll try to 
unify it.

Best regards,
Vladimir Ivanov