perms_syncer: fix logged counts and move up docstring
Created by: unknwon
The call of SetRepoPendingPermissions
would reset p.UserIDs
in place, so we were only logging the count of pending users.
Also move up docstring of GrantPendingPermissions
to its interface, I think it was overlooked.
Discovered while working on https://github.com/sourcegraph/customer/issues/993.
Test plan
Manual testing and unit tests.