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

lib/Serialization/ModuleFile.h

@@ -347,6 +347,12 @@ public:
   ///
   /// Note that this may cause other decls to load as well.
   void loadDeclsConformingTo(KnownProtocolKind kind);
+  
+  /// Reports all class members in the module to the given consumer.
+  ///
+  /// This is intended for use with id-style lookup and code completion.
+  void lookupClassMembers(Module::AccessPathTy accessPath,
+                          VisibleDeclConsumer &consumer);
 };
 
 class SerializedModule : public LoadedModule {