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>

http3/internal/testdata/cert_test.go

@@ -0,0 +1,28 @@
+package testdata
+
+import (
+	"crypto/tls"
+	"io"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestCertificates(t *testing.T) {
+	ln, err := tls.Listen("tcp", "localhost:4433", GetTLSConfig())
+	require.NoError(t, err)
+
+	go func() {
+		conn, err := ln.Accept()
+		require.NoError(t, err)
+		defer conn.Close()
+		_, err = conn.Write([]byte("foobar"))
+		require.NoError(t, err)
+	}()
+
+	conn, err := tls.Dial("tcp", "localhost:4433", &tls.Config{RootCAs: GetRootCA()})
+	require.NoError(t, err)
+	data, err := io.ReadAll(conn)
+	require.NoError(t, err)
+	require.Equal(t, "foobar", string(data))
+}