rem: usr: Restrict views to the Internet (IN) class

Views could previously be declared in classes other than Internet (IN),
but that support was inconsistent — ``named-checkconf`` accepted configurations
that ``named`` then refused to load.  Views are now restricted to class IN, and
both tools reject any other class.  Configurations declaring a non-IN view
must drop the class to keep working.

Merge branch '5784-improve-class-handling' into 'main'

See merge request isc-projects/bind9!12163