chg: usr: Parent-centric resolver

The `named` resolver now uses a separate "delegation database" to store zone referral data instead of the DNS cache. This new database holds the NS RRset on the parent side of a zone cut, as well as necessary glue records that were included in the referral. The NS RRset from the child side is cached in the DNS cache and is not used for name resolution.

This will be a step toward simplifying resolver logic and also supporting DELEG referrals.

Closes #3311

Merge branch 'colin/deleg-resolver' into 'main'

See merge request isc-projects/bind9!11621