go/scanner: add (*Scanner).End()

// This program demonstrates the new (*Scanner).End() method.
// It scans a simple Go source string and prints the position after the last token.
package main

import (
	"fmt"
	"go/scanner"
	"go/token"
)

func main() {
	src := []byte("package main\nfunc main() {}")
	fset := token.NewFileSet()
	file := fset.AddFile("", fset.Base(), len(src))

	var s scanner.Scanner
	s.Init(file, src, nil, scanner.ScanComments)

	// Scan all tokens.
	for {
		pos, tok, lit := s.Scan()
		if tok == token.EOF {
			break
		}
		fmt.Printf("token: %s, pos: %v, lit: %q\n", tok, pos, lit)
	}

	// After scanning, End() gives the position after the last token.
	endPos := s.End()
	fmt.Printf("End position: %v (offset %d)\n", endPos, file.Offset(endPos))
}