Add Go 1.20 errors.Join support

[StevenACoffman]

(Edit knz) Informs #99 and cockroachdb/cockroach#97799

(Note: the work in this PR is important but not sufficient to handle the Go 1.20 changes - we need to extend the other components to properly support multierrors from other packages in network serialization/deserialization)

All errors using cockroachdb/errors that are combined using Go 1.20 std lib errors.Join will lose the stacktrace when you fmt.Printf("%+v\n", err) on the joined error. Also, without native errors.Join support, this library is not a drop in replacement for the Go 1.20 stdlib errors package.

This PR adds errors.Join from Go 1.20 stdlib, but with a Format() method so joined errors honor the format verbs. Joined errors are printed verbosely indexed in square brackets like [0], to differentiate them from the parenthetical indexing (0) of wrapped errors.

[0]:
  (1) Another bad thing happened: Something went wrong
    -- Stack trace:
    | [...repeated from below...]
  Wraps: (2) Another bad thing happened: Something went wrong
  Wraps: (3) Something went wrong
    -- Stack trace:main.foo
    |   _example/main.go:22
    | main.bar
    |   _example/main.go:26
    | main.main
    |   _example/main.go:36
    | runtime.main
    |   /Users/steve/.asdf/installs/golang/1.20.2/go/src/runtime/proc.go:250
  Wraps: (4) Something went wrong
  Error types: (1) *errors.withStack (2) *errors.wrapper (3) *errors.withStack (4) main.ErrMyError
    -- Stack trace:main.main
    |   _example/main.go:38
[1]:
  (1) Yet another bad thing happened: Something went wrong
    -- Stack trace:
    | [...repeated from below...]
  Wraps: (2) Yet another bad thing happened: Something went wrong
  Wraps: (3) Something went wrong
    -- Stack trace:main.foo
    |   _example/main.go:22
    | main.baz
    |   _example/main.go:31
    | main.main
    |   _example/main.go:40
    | runtime.main
    |   /Users/steve/.asdf/installs/golang/1.20.2/go/src/runtime/proc.go:250
  Wraps: (4) Something went wrong
  Error types: (1) *errors.withStack (2) *errors.wrapper (3) *errors.withStack (4) main.ErrMyError
    -- Stack trace:main.main
    |   _example/main.go:40

This PR is not meant to be merged as is, and is more for discussion (and is hopefully helpful rather than just annoying 😬 ).

It currently leans on Go 1.20 std lib pkg fmt's new func FormatString(State, int32) string fmt: add FormatString(State) string #51668, rather than using the cockroachdb/errors internal format forwarding. As a result, this current implementation depends on Go 1.20+.

It is likely that backwards compatibility with pre-Go 1.20 is desirable, so this Format() would need to be reworked to use this library's errbase.Formatter and errbase.SafeFormatter to avoid that.

---

This change is 

[cockroach-teamcity]

All committers have signed the CLA.

[StevenACoffman]

This is an example program which generates the example output above to play with how to format output when errors.Join combines with errors.With and errors.WithStack:

// ErrMyError is an error that can be returned from a public API.
type ErrMyError struct {
    Msg string
}

func (e ErrMyError) Error() string {
    return e.Msg
}

func foo() error {
    // Attach stack trace to the sentinel error.
    return errors.WithStack(ErrMyError{Msg: "Something went wrong"})
}

func bar() error {
    withErr := errors.With(foo(), errors.New("Another bad thing happened"))
    return errors.WithStack(withErr)
}

func baz() error {
    withErr := errors.With(foo(), errors.New("Yet another bad thing happened"))
    return errors.WithStack(withErr)
}

func main() {
    myErr := bar()
    fmt.Println("Doing something")
    err := errors.WithStack(myErr)

    myOtherErr := errors.WithStack(baz())

    joinErr := errors.Join(err, myOtherErr)
    fmt.Println("\n\n---withStackBar")
    fmt.Printf("%+v\n", err)
    fmt.Println("\n\n---baz")
    fmt.Printf("%+v\n", myOtherErr)
    fmt.Println("\n\n---joinErr")
    fmt.Printf("%+v\n", joinErr)
}

[lexfrei]

@knz any news on this?

[knz]

In progress.

[dhartunian]

@StevenACoffman I incorporated your changes in separate branch PRs where I was compiling 1.20 compatibility work. Closing this PR since it's now merged. Thanks for the contribution. New releases will publish shortly with 1.20 support.