Add support for SVCB/HTTPS DNS records

[scalablecory]

SVCB/HTTPS is useful for HttpClient -- it will significantly reduce the time it takes to establish an HTTP/3 connection, as well as supply data needed for ECH, Alt-Svc, and HSTS-like features.

The next release of Safari is expected to support these, so there is some level of traction here.

Note our current name resolution does not provide the needed APIs to get this info; we might consider doing #19443 along with this, even as an internal-only version to support HttpClient.

One complication to consider here is that we would no longer rely on the OS's DNS cache.

[ghost]

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[scalablecory]

This is now entering the WGLC part of standards process. We should start looking at this as part of any DNS client efforts.

[karelz]

Triage: Should be part of DNS client #19443 as stated above. Not must have for 7.0 at this point.