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).

src/os/file_other.go

@@ -42,6 +42,14 @@ func NewFile(fd uintptr, name string) *File {
 	return &File{&file{handle: stdioFileHandle(fd), name: name}}
 }
 
+// Rename renames (moves) oldpath to newpath.
+// If newpath already exists and is not a directory, Rename replaces it.
+// OS-specific restrictions may apply when oldpath and newpath are in different directories.
+// If there is an error, it will be of type *LinkError.
+func Rename(oldpath, newpath string) error {
+	return ErrNotImplemented
+}
+
 // Read reads up to len(b) bytes from machine.Serial.
 // It returns the number of bytes read and any error encountered.
 func (f stdioFileHandle) Read(b []byte) (n int, err error) {