Add network device driver model, netdev

This PR adds a network device driver model called netdev. There will be a companion PR for TinyGo drivers to update the netdev drivers and network examples. This PR covers the core "net" package.

An RFC for the work is here: #tinygo-org/drivers#487. Some things have changed from the RFC, but nothing major.

The "net" package is a partial port of Go's "net" package, version 1.19.3. The src/net/README file has details on what is modified from Go's "net" package.

Most "net" features are working as they would in normal Go. TCP/UDP/TLS protocol support is there. As well as HTTP client and server support. Standard Go network packages such as golang.org/x/net/websockets and Paho MQTT client work as-is. Other packages are likely to work as-is.

Testing results are here (https://docs.google.com/spreadsheets/d/e/2PACX-1vT0cCjBvwXf9HJf6aJV2Sw198F2ief02gmbMV0sQocKT4y4RpfKv3dh6Jyew8lQW64FouZ8GwA2yjxI/pubhtml?gid=1013173032&single=true).

http/http.go

@@ -0,0 +1,161 @@
+// TINYGO: The following is copied from Go 1.19.3 official implementation.
+
+// Copyright 2016 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.
+
+//go:generate bundle -o=h2_bundle.go -prefix=http2 -tags=!nethttpomithttp2 golang.org/x/net/http2
+
+package http
+
+import (
+	"io"
+	"strconv"
+	"strings"
+	"time"
+	"unicode/utf8"
+
+	"golang.org/x/net/http/httpguts"
+)
+
+// incomparable is a zero-width, non-comparable type. Adding it to a struct
+// makes that struct also non-comparable, and generally doesn't add
+// any size (as long as it's first).
+type incomparable [0]func()
+
+// maxInt64 is the effective "infinite" value for the Server and
+// Transport's byte-limiting readers.
+const maxInt64 = 1<<63 - 1
+
+// aLongTimeAgo is a non-zero time, far in the past, used for
+// immediate cancellation of network operations.
+var aLongTimeAgo = time.Unix(1, 0)
+
+// omitBundledHTTP2 is set by omithttp2.go when the nethttpomithttp2
+// build tag is set. That means h2_bundle.go isn't compiled in and we
+// shouldn't try to use it.
+var omitBundledHTTP2 bool
+
+// TODO(bradfitz): move common stuff here. The other files have accumulated
+// generic http stuff in random places.
+
+// contextKey is a value for use with context.WithValue. It's used as
+// a pointer so it fits in an interface{} without allocation.
+type contextKey struct {
+	name string
+}
+
+func (k *contextKey) String() string { return "net/http context value " + k.name }
+
+// Given a string of the form "host", "host:port", or "[ipv6::address]:port",
+// return true if the string includes a port.
+func hasPort(s string) bool { return strings.LastIndex(s, ":") > strings.LastIndex(s, "]") }
+
+// removeEmptyPort strips the empty port in ":port" to ""
+// as mandated by RFC 3986 Section 6.2.3.
+func removeEmptyPort(host string) string {
+	if hasPort(host) {
+		return strings.TrimSuffix(host, ":")
+	}
+	return host
+}
+
+func isNotToken(r rune) bool {
+	return !httpguts.IsTokenRune(r)
+}
+
+// stringContainsCTLByte reports whether s contains any ASCII control character.
+func stringContainsCTLByte(s string) bool {
+	for i := 0; i < len(s); i++ {
+		b := s[i]
+		if b < ' ' || b == 0x7f {
+			return true
+		}
+	}
+	return false
+}
+
+func hexEscapeNonASCII(s string) string {
+	newLen := 0
+	for i := 0; i < len(s); i++ {
+		if s[i] >= utf8.RuneSelf {
+			newLen += 3
+		} else {
+			newLen++
+		}
+	}
+	if newLen == len(s) {
+		return s
+	}
+	b := make([]byte, 0, newLen)
+	for i := 0; i < len(s); i++ {
+		if s[i] >= utf8.RuneSelf {
+			b = append(b, '%')
+			b = strconv.AppendInt(b, int64(s[i]), 16)
+		} else {
+			b = append(b, s[i])
+		}
+	}
+	return string(b)
+}
+
+// NoBody is an io.ReadCloser with no bytes. Read always returns EOF
+// and Close always returns nil. It can be used in an outgoing client
+// request to explicitly signal that a request has zero bytes.
+// An alternative, however, is to simply set Request.Body to nil.
+var NoBody = noBody{}
+
+type noBody struct{}
+
+func (noBody) Read([]byte) (int, error)         { return 0, io.EOF }
+func (noBody) Close() error                     { return nil }
+func (noBody) WriteTo(io.Writer) (int64, error) { return 0, nil }
+
+var (
+	// verify that an io.Copy from NoBody won't require a buffer:
+	_ io.WriterTo   = NoBody
+	_ io.ReadCloser = NoBody
+)
+
+// PushOptions describes options for Pusher.Push.
+type PushOptions struct {
+	// Method specifies the HTTP method for the promised request.
+	// If set, it must be "GET" or "HEAD". Empty means "GET".
+	Method string
+
+	// Header specifies additional promised request headers. This cannot
+	// include HTTP/2 pseudo header fields like ":path" and ":scheme",
+	// which will be added automatically.
+	Header Header
+}
+
+// Pusher is the interface implemented by ResponseWriters that support
+// HTTP/2 server push. For more background, see
+// https://tools.ietf.org/html/rfc7540#section-8.2.
+type Pusher interface {
+	// Push initiates an HTTP/2 server push. This constructs a synthetic
+	// request using the given target and options, serializes that request
+	// into a PUSH_PROMISE frame, then dispatches that request using the
+	// server's request handler. If opts is nil, default options are used.
+	//
+	// The target must either be an absolute path (like "/path") or an absolute
+	// URL that contains a valid host and the same scheme as the parent request.
+	// If the target is a path, it will inherit the scheme and host of the
+	// parent request.
+	//
+	// The HTTP/2 spec disallows recursive pushes and cross-authority pushes.
+	// Push may or may not detect these invalid pushes; however, invalid
+	// pushes will be detected and canceled by conforming clients.
+	//
+	// Handlers that wish to push URL X should call Push before sending any
+	// data that may trigger a request for URL X. This avoids a race where the
+	// client issues requests for X before receiving the PUSH_PROMISE for X.
+	//
+	// Push will run in a separate goroutine making the order of arrival
+	// non-deterministic. Any required synchronization needs to be implemented
+	// by the caller.
+	//
+	// Push returns ErrNotSupported if the client has disabled push or if push
+	// is not supported on the underlying connection.
+	Push(target string, opts *PushOptions) error
+}