internal/godoc/dochtml: use natural sorting for items

This ensures that simd/archsimd package items are sorted nicely.
For example:

  "Uint8x64" < "Uint32x16" < "Uint64x8"

Fixes golang/go#77160

Change-Id: Ie08696262496e226120ae1b31ca81e02b7f20c65
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/736561
Auto-Submit: Sean Liao <sean@liao.dev>
kokoro-CI: kokoro <noreply+kokoro@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Ethan Lee <ethanalee@google.com>
Reviewed-by: Sean Liao <sean@liao.dev>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

1 files changed, 55 insertions, 0 deletions

diff --git a/internal/godoc/dochtml/testdata/order.go b/internal/godoc/dochtml/testdata/order.go
new file mode 100644
index 00000000..b8a82bfd
--- /dev/null
+++ b/internal/godoc/dochtml/testdata/order.go
@@ -0,0 +1,55 @@
+// Copyright 2026 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package order exercises natural sorting of symbols.
+package order
+
+// Uint32x16 represents a 128-bit unsigned integer.
+type Uint32x16 struct {
+	data [16]uint32
+}
+
+// AsUint8x64 converts a Uint32x16 to a Uint8x64.
+func (u Uint32x16) AsUint8x64() Uint8x64 {
+	return Uint8x64{}
+}
+
+// AsUint64x8 converts a Uint32x16 to a Uint64x8.
+func (u Uint32x16) AsUint64x8() Uint8x64 {
+	return Uint64x8{}
+}
+
+// Uint8x64 represents a 128-bit unsigned integer.
+type Uint8x64 struct {
+	data [64]uint8
+}
+
+// AsUint32x16 converts a Uint8x64 to a Uint32x16.
+func (u Uint8x64) AsUint32x16() Uint32x16 {
+	return Uint32x16{}
+}
+
+// AsUint64x8 converts a Uint8x64 to a Uint64x8.
+func (u Uint8x64) AsUint64x8() Uint64x8 {
+	return Uint64x8{}
+}
+
+// Uint64x8 represents a 128-bit unsigned integer.
+type Uint64x8 struct {
+	data [8]uint64
+}
+
+// AsUint8x64 converts a Uint64x8 to a Uint8x64.
+func (u Uint64x8) AsUint8x64() Uint8x64 {
+	return Uint8x64{}
+}
+
+// AsUint32x16 converts a Uint64x8 to a Uint32x16.
+func (u Uint64x8) AsUint32x16() Uint32x16 {
+	return Uint32x16{}
+}
+
+func ExampleUint64x8_AsUint32x16() {}
+
+func ExampleUint64x8_AsUint8x64() {}