swift234

Add lookupClassMembers for use in id-style dynamic lookup.

With this, we can now get a list of all class members* available in the
current translation unit, which will be necessary for doing id-style
dynamic lookup (inferring which method you're referring to when the base
type is some magic "dynamic lookup" type).

* Including members of protocols, since a class we don't know about could
have implemented the protocol.

Since there is no code currently using this, I've added a new mode to
swift-ide-test to just dump all class members -- what will eventually
happen when you code complete on a dynamic lookup type. This mode will
go away once the other pieces of id-style lookup are in place.

Swift SVN r7287