[9.20] fix: usr: Reject record sets too large to serve in DNS

[9.20] fix: usr: Reject record sets too large to serve in DNS

When BIND was asked to store a record set whose total size exceeds
what fits in a DNS message, it would allocate memory and build the
structure, then fail later at response time. Such oversized record
sets are now rejected at the time of storage with an error, avoiding
wasted work on data that can never be served.

Backport of MR !11963

Merge branch 'backport-ondrej/harden-buflen-overflow-9.20' into 'bind-9.20'

See merge request isc-projects/bind9!11964