quic: add internal/quic package

This package will eventually contain an implementation of the QUIC
protocol. Place it under internal/ to begin with to avoid accidental
use while it is in an incomplete state.

For golang/go#58547

Change-Id: Ib3526e0bbe433e91283859913818d3e72fc194b6
Reviewed-on: https://go-review.googlesource.com/c/net/+/468402
Reviewed-by: Matt Layher <mdlayher@gmail.com>
Reviewed-by: Roland Shoemaker <roland@golang.org>
Run-TryBot: Matt Layher <mdlayher@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Damien Neil <dneil@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>

Author: neild

internal/quic/doc.go

@@ -0,0 +1,9 @@
+// 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 quic is an experimental, incomplete implementation of the QUIC protocol.
+// This package is a work in progress, and is not ready for use at this time.
+//
+// This package implements (or will implement) RFC 9000, RFC 9001, and RFC 9002.
+package quic