all: move internal/x to vendor/golang.org/x and revendor using 'go mod vendor'

This also updates the vendored-in versions of several packages: 'go
mod vendor' selects a consistent version of each module, but we had
previously vendored an ad-hoc selection of packages.

Notably, x/crypto/hkdf was previously vendored in at a much newer
commit than the rest of x/crypto. Bringing the rest of x/crypto up to
that commit introduced an import of golang.org/x/sys/cpu, which broke
the js/wasm build, requiring an upgrade of x/sys to pick up CL 165749.

Updates #30228
Updates #30241
Updates #25822

Change-Id: I5b3dbc232b7e6a048a158cbd8d36137af1efb711
Reviewed-on: https://go-review.googlesource.com/c/go/+/164623
Reviewed-by: Filippo Valsorda <filippo@golang.org>

src/net/dnsclient_unix_test.go

@@ -20,7 +20,7 @@ import (
 	"testing"
 	"time"
 
-	"internal/x/net/dns/dnsmessage"
+	"golang.org/x/net/dns/dnsmessage"
 )
 
 var goResolver = Resolver{PreferGo: true}