(#15559) Ensure SYSTEM has full control unless specified otherwise

 - When a file is managed, and the group and owner are not explicitly
   set, SYSTEM should always be granted full access
 - When the group or owner is set to SYSTEM, apply the specified mode
Merge branch 'ticket/master/15559-dont-remove-windows-SYSTEM-permissions'

* ticket/master/15559-dont-remove-windows-SYSTEM-permissions:
  (#15559) Ensure SYSTEM has full control unless specified otherwise