x/net/dns/dnsmessage: add https svcb dns types

[fortuna]

This change implements the proposal to add new DNS message types HTTPS and SVCB in the golang.org/x/net/dns/dnsmessage package, as described in golang/go#43790.

The implementation includes:

• New types TypeHTTPS and TypeSVCB.
• SVCBResource and HTTPSResource structs, with HTTPSResource embedding SVCBResource.
• SVCParam and SVCParamKey types for handling service parameters.
• pack and unpack methods for the new resource types.
• Integration into the Parser and Builder.
• Comprehensive tests, including for parameter handling logic.

I implemented the SVCB parsing code so that it performs only two allocations: one for the SVCParam[] slice, and one to hold the SVCParam values. A test was added to demonstrate that.

Fixes golang/go#43790

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Message from Gopher Robot:

Patch Set 1:

(1 comment)

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Message from Vinicius Fortuna:

Patch Set 1:

(1 comment)

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Patch Set 1:

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Message from Vinicius Fortuna:

Patch Set 6:

(1 comment)

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Message from Vinicius Fortuna:

Patch Set 6: Code-Review+1

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