swift-package-manager

[Utility] Migrate ad hoc `walk` clients to use localFS.

 - This just migrates clients outside the core convention system which only
   needed individual directory listings over.

 - This reapplies 4f3e7042 with a fix to add the additional hard coded
   test dependency for `Functional` on `Basic` which is required
   currently pending real support for specifying dependencies of test
   modules.