types/views: add MarshalJSONV2 to Slice

It helps, but not all the way.

                               │   before   │                  after                  │
                               │    B/op    │    B/op      vs base                    │
    JSONMarshalView/v1_slice-8   64.00 ± 0%   64.00 ± ∞ ¹        ~ (p=1.000 n=10+1) ²
    JSONMarshalView/v1_view-8    136.0 ± 0%   136.0 ± ∞ ¹        ~ (p=1.000 n=10+1) ²
    JSONMarshalView/v2_slice-8   64.00 ± 0%   64.00 ± ∞ ¹        ~ (p=1.000 n=10+1) ²
    JSONMarshalView/v2_view-8    136.0 ± 0%   112.0 ± ∞ ¹  -17.65% (n=10+1)

Updates tailscale/corp#14379
Updates tailscale/corp#21429 (new benchmark)

Change-Id: I891dd6a4db1a995ae1be14f8c5085629bb30b8da
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

cmd/derper/depaware.txt

@@ -10,6 +10,12 @@ tailscale.com/cmd/derper dependencies: (generated by github.com/tailscale/depawa
    L    github.com/coreos/go-iptables/iptables                       from tailscale.com/util/linuxfw
    W 💣 github.com/dblohm7/wingoes                                   from tailscale.com/util/winutil
         github.com/fxamacker/cbor/v2                                 from tailscale.com/tka
+        github.com/go-json-experiment/json                           from tailscale.com/types/views
+        github.com/go-json-experiment/json/internal                  from github.com/go-json-experiment/json+
+        github.com/go-json-experiment/json/internal/jsonflags        from github.com/go-json-experiment/json+
+        github.com/go-json-experiment/json/internal/jsonopts         from github.com/go-json-experiment/json+
+        github.com/go-json-experiment/json/internal/jsonwire         from github.com/go-json-experiment/json+
+        github.com/go-json-experiment/json/jsontext                  from github.com/go-json-experiment/json+
         github.com/golang/groupcache/lru                             from tailscale.com/net/dnscache
    L    github.com/google/nftables                                   from tailscale.com/util/linuxfw
    L 💣 github.com/google/nftables/alignedbuff                       from github.com/google/nftables/xt

cmd/stund/depaware.txt

@@ -2,6 +2,12 @@ tailscale.com/cmd/stund dependencies: (generated by github.com/tailscale/depawar
 
         github.com/beorn7/perks/quantile                             from github.com/prometheus/client_golang/prometheus
      💣 github.com/cespare/xxhash/v2                                 from github.com/prometheus/client_golang/prometheus
+        github.com/go-json-experiment/json                           from tailscale.com/types/views
+        github.com/go-json-experiment/json/internal                  from github.com/go-json-experiment/json+
+        github.com/go-json-experiment/json/internal/jsonflags        from github.com/go-json-experiment/json+
+        github.com/go-json-experiment/json/internal/jsonopts         from github.com/go-json-experiment/json+
+        github.com/go-json-experiment/json/internal/jsonwire         from github.com/go-json-experiment/json+
+        github.com/go-json-experiment/json/jsontext                  from github.com/go-json-experiment/json+
         github.com/google/uuid                                       from tailscale.com/util/fastuuid
      💣 github.com/prometheus/client_golang/prometheus               from tailscale.com/tsweb/promvarz
         github.com/prometheus/client_golang/prometheus/internal      from github.com/prometheus/client_golang/prometheus
@@ -128,6 +134,7 @@ tailscale.com/cmd/stund dependencies: (generated by github.com/tailscale/depawar
         embed                                                        from crypto/internal/nistec+
         encoding                                                     from encoding/json+
         encoding/asn1                                                from crypto/x509+
+        encoding/base32                                              from github.com/go-json-experiment/json
         encoding/base64                                              from encoding/json+
         encoding/binary                                              from compress/gzip+
         encoding/hex                                                 from crypto/x509+

cmd/tailscale/depaware.txt

@@ -9,6 +9,12 @@ tailscale.com/cmd/tailscale dependencies: (generated by github.com/tailscale/dep
    W 💣 github.com/dblohm7/wingoes                                   from github.com/dblohm7/wingoes/pe+
    W 💣 github.com/dblohm7/wingoes/pe                                from tailscale.com/util/winutil/authenticode
         github.com/fxamacker/cbor/v2                                 from tailscale.com/tka
+        github.com/go-json-experiment/json                           from tailscale.com/types/views
+        github.com/go-json-experiment/json/internal                  from github.com/go-json-experiment/json+
+        github.com/go-json-experiment/json/internal/jsonflags        from github.com/go-json-experiment/json+
+        github.com/go-json-experiment/json/internal/jsonopts         from github.com/go-json-experiment/json+
+        github.com/go-json-experiment/json/internal/jsonwire         from github.com/go-json-experiment/json+
+        github.com/go-json-experiment/json/jsontext                  from github.com/go-json-experiment/json+
         github.com/golang/groupcache/lru                             from tailscale.com/net/dnscache
    L    github.com/google/nftables                                   from tailscale.com/util/linuxfw
    L 💣 github.com/google/nftables/alignedbuff                       from github.com/google/nftables/xt

cmd/tailscaled/depaware.txt

@@ -90,11 +90,12 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
      💣 github.com/djherbis/times                                    from tailscale.com/drive/driveimpl
         github.com/fxamacker/cbor/v2                                 from tailscale.com/tka
         github.com/gaissmai/bart                                     from tailscale.com/net/tstun+
+        github.com/go-json-experiment/json                           from tailscale.com/types/views
         github.com/go-json-experiment/json/internal                  from github.com/go-json-experiment/json/internal/jsonflags+
         github.com/go-json-experiment/json/internal/jsonflags        from github.com/go-json-experiment/json/internal/jsonopts+
-        github.com/go-json-experiment/json/internal/jsonopts         from github.com/go-json-experiment/json/jsontext
-        github.com/go-json-experiment/json/internal/jsonwire         from github.com/go-json-experiment/json/jsontext
-        github.com/go-json-experiment/json/jsontext                  from tailscale.com/logtail
+        github.com/go-json-experiment/json/internal/jsonopts         from github.com/go-json-experiment/json/jsontext+
+        github.com/go-json-experiment/json/internal/jsonwire         from github.com/go-json-experiment/json/jsontext+
+        github.com/go-json-experiment/json/jsontext                  from tailscale.com/logtail+
    W 💣 github.com/go-ole/go-ole                                     from github.com/go-ole/go-ole/oleutil+
    W 💣 github.com/go-ole/go-ole/oleutil                             from tailscale.com/wgengine/winnet
    L 💣 github.com/godbus/dbus/v5                                    from tailscale.com/net/dns+

types/views/views.go

@@ -13,6 +13,9 @@ import (
 	"maps"
 	"slices"
 
+	jsonexp "github.com/go-json-experiment/json"
+	jsontext "github.com/go-json-experiment/json/jsontext"
+
 	"go4.org/mem"
 )
 
@@ -225,6 +228,13 @@ func (v Slice[T]) MarshalJSON() ([]byte, error) {
 	return json.Marshal(v.ж)
 }
 
+var _ jsonexp.MarshalerV2 = Slice[string]{nil}
+
+// MarshalJSON implements github.com/go-json-experiment/json.MarshalerV2.
+func (v Slice[T]) MarshalJSONV2(e *jsontext.Encoder, opts jsonexp.Options) error {
+	return jsonexp.MarshalEncode(e, v.ж, opts)
+}
+
 // UnmarshalJSON implements json.Unmarshaler.
 func (v *Slice[T]) UnmarshalJSON(b []byte) error {
 	return unmarshalSliceFromJSON(b, &v.ж)