Partially addresses #47424. Had to make changes to spec files because stubbing methods on frozen objects is a mess in RSpec and leads to failures: https://github.com/rspec/rspec-mocks/issues/1190
AccessTokenValidationService
String
API::Scope
- There's no need to use `API::Scope` for scopes that don't have `if` conditions, such as in `lib/gitlab/auth.rb`.
Gitlab::Scope
- To represent an authorization scope, such as `api` or `read_user` - This is a better abstraction than the hash we were previously using.