RFR: 8219816: Add IsArray/RemoveArray type traits utilities

[Kim Barrett]

> On Mar 4, 2019, at 4:48 AM, Per Liden <per.liden at oracle.com> wrote:
> Ah, good catch. Renamed accordingly. I'm not implementing remove_all_extents at this time, let's add that when there's a use case for it.
> 
> Updated webrev: http://cr.openjdk.java.net/~pliden/8219816/webrev.1
> 
> /Per

Not implementing remove_all_extents at this time is fine.

Looks good.