implement dnssec-awareness throughout code, and dane for incoming/outgoing mail delivery

the vendored dns resolver code is a copy of the go stdlib dns resolver, with
awareness of the "authentic data" (i.e. dnssec secure) added, as well as support
for enhanced dns errors, and looking up tlsa records (for dane). ideally it
would be upstreamed, but the chances seem slim.

dnssec-awareness is added to all packages, e.g. spf, dkim, dmarc, iprev. their
dnssec status is added to the Received message headers for incoming email.

but the main reason to add dnssec was for implementing dane. with dane, the
verification of tls certificates can be done through certificates/public keys
published in dns (in the tlsa records). this only makes sense (is trustworthy)
if those dns records can be verified to be authentic.

mox now applies dane to delivering messages over smtp. mox already implemented
mta-sts for webpki/pkix-verification of certificates against the (large) pool
of CA's, and still enforces those policies when present. but it now also checks
for dane records, and will verify those if present. if dane and mta-sts are
both absent, the regular opportunistic tls with starttls is still done. and the
fallback to plaintext is also still done.

mox also makes it easy to setup dane for incoming deliveries, so other servers
can deliver with dane tls certificate verification. the quickstart now
generates private keys that are used when requesting certificates with acme.
the private keys are pre-generated because they must be static and known during
setup, because their public keys must be published in tlsa records in dns.
autocert would generate private keys on its own, so had to be forked to add the
option to provide the private key when requesting a new certificate. hopefully
upstream will accept the change and we can drop the fork.

with this change, using the quickstart to setup a new mox instance, the checks
at internet.nl result in a 100% score, provided the domain is dnssec-signed and
the network doesn't have any issues.

vendor/golang.org/x/tools/internal/typeparams/coretype.go

@@ -81,13 +81,13 @@ func CoreType(T types.Type) types.Type {
 // restrictions may be arbitrarily complex. For example, consider the
 // following:
 //
-//  type A interface{ ~string|~[]byte }
+//	type A interface{ ~string|~[]byte }
 //
-//  type B interface{ int|string }
+//	type B interface{ int|string }
 //
-//  type C interface { ~string|~int }
+//	type C interface { ~string|~int }
 //
-//  type T[P interface{ A|B; C }] int
+//	type T[P interface{ A|B; C }] int
 //
 // In this example, the structural type restriction of P is ~string|int: A|B
 // expands to ~string|~[]byte|int|string, which reduces to ~string|~[]byte|int,

vendor/golang.org/x/tools/internal/typeparams/termlist.go

@@ -30,7 +30,7 @@ func (xl termlist) String() string {
 	var buf bytes.Buffer
 	for i, x := range xl {
 		if i > 0 {
-			buf.WriteString(" ∪ ")
+			buf.WriteString(" | ")
 		}
 		buf.WriteString(x.String())
 	}

vendor/golang.org/x/tools/internal/typeparams/typeterm.go

@@ -10,11 +10,10 @@ import "go/types"
 
 // A term describes elementary type sets:
 //
-//   ∅:  (*term)(nil)     == ∅                      // set of no types (empty set)
-//   𝓤:  &term{}          == 𝓤                      // set of all types (𝓤niverse)
-//   T:  &term{false, T}  == {T}                    // set of type T
-//  ~t:  &term{true, t}   == {t' | under(t') == t}  // set of types with underlying type t
-//
+//	 ∅:  (*term)(nil)     == ∅                      // set of no types (empty set)
+//	 𝓤:  &term{}          == 𝓤                      // set of all types (𝓤niverse)
+//	 T:  &term{false, T}  == {T}                    // set of type T
+//	~t:  &term{true, t}   == {t' | under(t') == t}  // set of types with underlying type t
 type term struct {
 	tilde bool // valid if typ != nil
 	typ   types.Type

vendor/golang.org/x/tools/internal/typesinternal/objectpath.go

@@ -0,0 +1,24 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package typesinternal
+
+import "go/types"
+
+// This file contains back doors that allow gopls to avoid method sorting when
+// using the objectpath package.
+//
+// This is performance-critical in certain repositories, but changing the
+// behavior of the objectpath package is still being discussed in
+// golang/go#61443. If we decide to remove the sorting in objectpath we can
+// simply delete these back doors. Otherwise, we should add a new API to
+// objectpath that allows controlling the sorting.
+
+// SkipEncoderMethodSorting marks enc (which must be an *objectpath.Encoder) as
+// not requiring sorted methods.
+var SkipEncoderMethodSorting func(enc interface{})
+
+// ObjectpathObject is like objectpath.Object, but allows suppressing method
+// sorting.
+var ObjectpathObject func(pkg *types.Package, p string, skipMethodSorting bool) (types.Object, error)

vendor/golang.org/x/tools/internal/typesinternal/types.go

@@ -11,8 +11,6 @@ import (
 	"go/types"
 	"reflect"
 	"unsafe"
-
-	"golang.org/x/tools/go/types/objectpath"
 )
 
 func SetUsesCgo(conf *types.Config) bool {
@@ -52,17 +50,3 @@ func ReadGo116ErrorData(err types.Error) (code ErrorCode, start, end token.Pos,
 }
 
 var SetGoVersion = func(conf *types.Config, version string) bool { return false }
-
-// SkipEncoderMethodSorting marks the encoder as not requiring sorted methods,
-// as an optimization for gopls (which guarantees the order of parsed source files).
-//
-// TODO(golang/go#61443): eliminate this parameter one way or the other.
-//
-//go:linkname SkipEncoderMethodSorting golang.org/x/tools/go/types/objectpath.skipMethodSorting
-func SkipEncoderMethodSorting(enc *objectpath.Encoder)
-
-// ObjectpathObject is like objectpath.Object, but allows suppressing method
-// sorting (which is not necessary for gopls).
-//
-//go:linkname ObjectpathObject golang.org/x/tools/go/types/objectpath.object
-func ObjectpathObject(pkg *types.Package, p objectpath.Path, skipMethodSorting bool) (types.Object, error)