swift234

Move protocol-conformance computation into Module::lookupConformance().

Introduce an AST operation that, given a type and a protocol, determines
whether the type conforms to the protocol and produces the protocol
conformance structure. Previously, this operation was only available
on the type checker, requiring many callbacks from the AST to the type
checker during AST substitution operations (for example).

Now, we only call back into the type checker when we hit a case where
we see an explicit conformance in the AST, but the actual
ProtocolConformance object has not yet been built due to lazy type
checking.

Note that we still require a resolver (i.e., a TypeChecker) in a few
places, although we shouldn't need it outside of lazy type
checking. I'll loosen up the restrictions next.

There's a minor diagnostics regression here that will be cleaned up in
a future commit.


Swift SVN r8129