swift234

Rework getReexportedModules to optionally find all imported modules.

...instead of just those that are re-exported. This will be used for
autolinking (and probably few other places).

As part of this, we get two name changes:
  (1) Module::getReexportedModules -> getImportedModules
  (2) TranslationUnit::getImportedModules -> getImports

The latter doesn't just get modules-plus-access-paths; it also includes
whether or not the import is re-exported. Mainly, though, it just didn't
seem like a good idea to overload this name when the two functions aren't
really related.

No tests yet, will come with autolinking.

Swift SVN r7487