new: test: Add build-time check for unregistered rdata files

Fail at meson configure if an rdata source file in lib/dns/rdata is not
registered in dns_header_depfiles, so edits no longer silently skip
header regeneration (as happened with brid, dsync, hhit, and wallet).

Assisted-by: Claude:claude-opus-4-8
Merge branch 'mnowak/check-rdata-registration' into 'main'

See merge request isc-projects/bind9!12219