fmterrorfix: tooling to automatically rewrite fmt.Errorf to errors.New if needed

Implements a CLI tool that'll traverse a directory, find all patterns
matching fmt.Errorf without format specifiers and replace in-place such
with errors.New. For example for the Go standard library

```shell
go run main.go $GOPATH/src/go.googlesource.com
```

Updates golang/go#52696

Author: odeke-em

fmterrorffix/go.mod

@@ -0,0 +1,3 @@
+module github.com/orijtech/otils/fmterrorffix
+
+go 1.19

fmterrorffix/main.go

@@ -0,0 +1,87 @@
+package main
+
+import (
+	"io"
+	"io/fs"
+	"os"
+	"path/filepath"
+	"regexp"
+	"strings"
+)
+
+var reBadFmtErrorf = regexp.MustCompile("(?P<fmt>fmt.Errorf)\\((?P<args>(\"[^%]*\"|`[^%]*`))\\)")
+
+func main() {
+	dirPath := "."
+	if len(os.Args) > 1 {
+		dirPath = os.Args[1]
+	}
+
+	targetsCh := make(chan string, 10)
+	go func() {
+		defer close(targetsCh)
+
+		err := filepath.WalkDir(dirPath, func(path string, d fs.DirEntry, err error) error {
+			if err != nil {
+				panic(err)
+				return err
+			}
+			if d.IsDir() {
+				return nil
+			}
+			if !strings.HasSuffix(d.Name(), ".go") {
+				return nil
+			}
+			if strings.Contains(path, "vendor") {
+				return nil
+			}
+
+			targetsCh <- path
+			return nil
+		})
+		if err != nil {
+			panic(err)
+		}
+	}()
+
+	for path := range targetsCh {
+		if err := searchAndReplace(path); err != nil {
+			panic(err)
+		}
+	}
+}
+
+func searchAndReplace(fullPath string) error {
+	f, err := os.Open(fullPath)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	blob, err := io.ReadAll(f)
+	if err != nil {
+		return err
+	}
+
+	if !reBadFmtErrorf.Match(blob) {
+		return nil
+	}
+
+	// Preserve the prior permissions.
+	fi, err := f.Stat()
+	f.Close()
+	if err != nil {
+		return nil
+	}
+	wf, err := os.OpenFile(fullPath, os.O_WRONLY, fi.Mode())
+	if err != nil {
+		return err
+	}
+	defer wf.Close()
+
+	ml := reBadFmtErrorf.ReplaceAll(blob, []byte("errors.New(${args})"))
+	if _, err := wf.Write(ml); err != nil {
+		panic(err)
+	}
+	return nil
+}