Modernize OAuthserver and provide more context on "no permission" exception

Summary:
Ref T7173. Depends on D14049. Now that Phacility can install custom exception handlers, this puts enough information on the exception so that we can figure out what to do with it.

• Generally modernize some of this code.
• Add some more information to PolicyExceptions so the new RequestExceptionHandler can handle them properly.

Test Plan: Failed authorizations, then succeeded authorizations. See next diff.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T7173

Differential Revision: https://secure.phabricator.com/D14050