Change most functions in `ratelimits` to use full ACMEIdentifier(s) as
arguments, instead of using their values as strings. This makes the
plumbing from other packages more consistent, and allows us to:
Rename `FQDNsToETLDsPlusOne` to `coveringIdentifiers` and handle IP
identifiers, parsing IPv6 addresses into their covering /64 prefixes for
CertificatesPerDomain[PerAccount] bucket keys.
Port improved IP/CIDR validation logic to NewRegistrationsPerIPAddress &
PerIPv6Range.
Rename `domain` parts of bucket keys to either `identValue` or
`domainOrCIDR`.
Rename other internal functions to clarify that they now handle
identifier values, not just domains.
Add the new reserved IPv6 address range from RFC 9780.
For deployability, don't (yet) rename rate limits themselves; and
because it remains the name of the database table, preserve the term
`fqdnSets`.
Fixes#8223
Part of #7311
Move `IsReservedIP` and its supporting vars from `bdns` to `policy`.
Rewrite `IsReservedIP` to:
* Use `netip` because `netip.Prefix` can be used as a map key, allowing
us to define prefix lists more elegantly. This will enable future work
to import prefix lists from IANA's primary source data.
* Return an error including the reserved network's name.
Refactor `IsReservedIP` tests to be table-based.
Fixes#8040
James Renken