http3: remove dependency on quic internal packages (#5256)

* Remove http3 dependency on quic internal packages

Remove the dependency on internal/protocol from the http3 package. This
makes it possible for a forked http3 to use the mainline quic-go
package.

* Address review comments

* Fix syntax

* Use broader pattern for http3 directory

* Copy internal/testdata

* Replace perspective with bool

* clone the supported version slice

---------

Co-authored-by: Marten Seemann <martenseemann@gmail.com>

interface.go

@@ -5,6 +5,7 @@ import (
 	"crypto/tls"
 	"errors"
 	"net"
+	"slices"
 	"time"
 
 	"github.com/quic-go/quic-go/internal/handshake"
@@ -25,6 +26,12 @@ const (
 	Version2 = protocol.Version2
 )
 
+// SupportedVersions returns the support versions, sorted in descending order of preference.
+func SupportedVersions() []Version {
+	// clone the slice to prevent the caller from modifying the slice
+	return slices.Clone(protocol.SupportedVersions)
+}
+
 // A ClientToken is a token received by the client.
 // It can be used to skip address validation on future connection attempts.
 type ClientToken struct {