swift234

Sema: Clean up name lookup and fix a couple of bugs

Previously, qualified lookup would use a metatype to signal
to the LookupResultBuilder that conformance checks should not
be used to resolve protocol members found with a concrete
type base. This is too subtle for my taste. Add an explicit
flag and clean up some usages, fixing <rdar://problem/16123805>.

Also, clean up the 'CheckProtocolMembers' flag. We now set
when the base type is an archetype, and correctly handle
the concept of an abstract conformance. This finally
fixes <rdar://problem/22776964>.