swift234

Looking up conformances for a type isn't always a public use of the type.

Specifically, it's not when
- the conformance is being used within a function body (test included)
- the conformance is being used for or within a private type (test included)
- the conformance is being used to generate a diagnostic string

We're still a bit imprecise in some places (checking ObjC bridging), but
in general this means less of an issue for checking literals.

Swift SVN r23700