encoding/json/v2: use slices.Sort directly

This is semantically identical and just a cleanup.

Prior to #63397, JSON object names were sorted according to UTF-16
to match the semantic of RFC 8785, but there were a number of
objections in the discussion to using that as the sorting order.

In https://github.com/go-json-experiment/json/pull/121,
we switched to sorting by UTF-8, which matches the behavior
of v1 and avoids an option to toggle the behavior.
However, we should have deleted the stringSlice.Sort method
and just directly called slices.Sort.

From a principled perspective, both UTF-16 and UTF-8 are
reasonable ways to sort JSON object names.
RFC 8259 specifies that the entire JSON text is encoded as UTF-8.
However, the way JSON strings are encoded requires escaping
Unicode codepoints according to UTF-16 surragate halves
(a quirk of JavaScript inherited by JSON).
Thus, JSON is inconsistently both UTF-8 and UTF-16.

Change-Id: Id92b5cc20efe4201827e9d3fccf24ccf894d3e60
Reviewed-on: https://go-review.googlesource.com/c/go/+/713522
Reviewed-by: Johan Brandhorst-Satzkorn <johan.brandhorst@gmail.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
TryBot-Bypass: Damien Neil <dneil@google.com>
Auto-Submit: Damien Neil <dneil@google.com>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Reviewed-by: Damien Neil <dneil@google.com>

src/encoding/json/v2/arshal.go

@@ -11,8 +11,6 @@ import (
 	"encoding"
 	"io"
 	"reflect"
-	"slices"
-	"strings"
 	"sync"
 	"time"
 
@@ -575,7 +573,3 @@ func putStrings(s *stringSlice) {
 	}
 	stringsPools.Put(s)
 }
-
-func (ss *stringSlice) Sort() {
-	slices.SortFunc(*ss, func(x, y string) int { return strings.Compare(x, y) })
-}

src/encoding/json/v2/arshal_any.go

@@ -10,6 +10,7 @@ import (
 	"cmp"
 	"math"
 	"reflect"
+	"slices"
 	"strconv"
 
 	"encoding/json/internal"
@@ -153,7 +154,7 @@ func marshalObjectAny(enc *jsontext.Encoder, obj map[string]any, mo *jsonopts.St
 			(*names)[i] = name
 			i++
 		}
-		names.Sort()
+		slices.Sort(*names)
 		for _, name := range *names {
 			if err := enc.WriteToken(jsontext.String(name)); err != nil {
 				return err

src/encoding/json/v2/arshal_default.go

@@ -843,7 +843,7 @@ func makeMapArshaler(t reflect.Type) *arshaler {
 					k.SetIterKey(iter)
 					(*names)[i] = k.String()
 				}
-				names.Sort()
+				slices.Sort(*names)
 				for _, name := range *names {
 					if err := enc.WriteToken(jsontext.String(name)); err != nil {
 						return err

src/encoding/json/v2/arshal_inlined.go

@@ -11,6 +11,7 @@ import (
 	"errors"
 	"io"
 	"reflect"
+	"slices"
 
 	"encoding/json/internal/jsonflags"
 	"encoding/json/internal/jsonopts"
@@ -146,7 +147,7 @@ func marshalInlinedFallbackAll(enc *jsontext.Encoder, va addressableValue, mo *j
 				mk.SetIterKey(iter)
 				(*names)[i] = mk.String()
 			}
-			names.Sort()
+			slices.Sort(*names)
 			for _, name := range *names {
 				mk.SetString(name)
 				if err := marshalKey(mk); err != nil {