swift234

Make deserialization of known protocol adopters lazy.

...by adding a new callback to ModuleLoader: loadDeclsConformingTo.
This is used only when the type checker doesn't have enough contextual
information to resolve an expression involving a literal, so it's
possible many *LiteralConvertible types will never be loaded.

Deserialization of types with conversion methods is still eager, since
there's no easy hook to tell when they're needed, but the list has been
renamed to refer to any decls that need to be eagerly deserialized, in
case we need it for other purposes in the future.

This probably won't help much in a real program, but it cuts the test
run time by about 5-10% in my build.

Swift SVN r7268