Enum path inference with `_Variant` syntax

[scottmcm]

I don't think using _Variant instead of _::Variant or .Variant really solves anything. Having it be ambiguous with a no-unused-variable-warning binding seems worse, to me.

To me, the blocker here has not been syntax, but the naming thing (which you did mention)

[Pre-RFC] Inferred Enum Type

To me, the awkward thing about adding this is that it could easily lead to needing to change the conventions for how variants are named. Something like make_webrequest(CookieHandling::Skip) is perfectly readable, but make_webrequest(_::Skip) is pretty confusing. So because the latter syntax doesn't exist, a variant name of Skip is reasonable today, but might not be good later. But if people end up wanting to do _::SkipCookies, that's the kind of repetitive naming (CookieHandling::SkipCookies)…

The syntax we could just pick one of the possible answers, if we really wanted.

But if .Yes could be AllowUnstable::Yes or Capturing::Yes or IsPattern::Yes, that's a more fundamental concern that's harder to resolve. I don't really know how to make progress on it.