refactor: move quicdialing base functionality to netxlite (#406)

Part of https://github.com/ooni/probe/issues/1505

internal/netxmocks/quic.go

@@ -0,0 +1,13 @@
+package netxmocks
+
+import "net"
+
+// QUICListener is a mockable netxlite.QUICListener.
+type QUICListener struct {
+	MockListen func(addr *net.UDPAddr) (net.PacketConn, error)
+}
+
+// Listen calls MockListen.
+func (ql *QUICListener) Listen(addr *net.UDPAddr) (net.PacketConn, error) {
+	return ql.MockListen(addr)
+}