internal/robustio: reimport from upstream

This imports robustio from the Go project at commit dc04f3ba1f25313bc9c97e728620206c235db9ee.

This replaces the remaining references to ioutil.

internal/robustio/UPSTREAM

@@ -3,4 +3,4 @@ It is mostly in sync with upstream according to the last commit we've looked at,
 with the exception of still using I/O functions that work with older Go versions.
 
 The last upstream commit we've looked at was:
-06ac303f6a14b133254f757e54599c48e3c2a4ad
+dc04f3ba1f25313bc9c97e728620206c235db9ee

internal/robustio/robustio.go

@@ -22,7 +22,7 @@ func Rename(oldpath, newpath string) error {
 	return rename(oldpath, newpath)
 }
 
-// ReadFile is like ioutil.ReadFile, but on Windows retries errors that may
+// ReadFile is like os.ReadFile, but on Windows retries errors that may
 // occur if the file is concurrently replaced.
 //
 // (See golang.org/issue/31247 and golang.org/issue/32188.)

internal/robustio/robustio_flaky.go

@@ -3,13 +3,11 @@
 // license that can be found in the LICENSE file.
 
 //go:build windows || darwin
-// +build windows darwin
 
 package robustio
 
 import (
 	"errors"
-	"io/ioutil"
 	"math/rand"
 	"os"
 	"syscall"
@@ -71,11 +69,11 @@ func rename(oldpath, newpath string) (err error) {
 	})
 }
 
-// readFile is like ioutil.ReadFile, but retries ephemeral errors.
+// readFile is like os.ReadFile, but retries ephemeral errors.
 func readFile(filename string) ([]byte, error) {
 	var b []byte
 	err := retry(func() (err error, mayRetry bool) {
-		b, err = ioutil.ReadFile(filename)
+		b, err = os.ReadFile(filename)
 
 		// Unlike in rename, we do not retry errFileNotFound here: it can occur
 		// as a spurious error, but the file may also genuinely not exist, so the

internal/robustio/robustio_other.go

@@ -3,7 +3,6 @@
 // license that can be found in the LICENSE file.
 
 //go:build !windows && !darwin
-// +build !windows,!darwin
 
 package robustio