Coding Style: Minor tweaks due to scoped enums

- Clarify that int constants should be unscoped enums.
- Require enum values to duplicate the enum's type only
  for unscoped enums.

Change-Id: Ibf63ada3a925c0fe0a364fd408cedc9638cf4708
Reviewed-by: hjk <hjk@theqtcompany.com>
Reviewed-by: Eike Ziller <eike.ziller@theqtcompany.com>