Expose public/ API as submodule (#23345)

* model -> public/model

* plugin -> public/plugin

* public/model/utils -> public/utils

* platform/shared/mlog -> public/shared/mlog

* platform/shared/i18n -> public/shared/i18n

* platform/shared/markdown -> public/shared/markdown

* platform/services/timezones -> public/shared/timezones

* channels/einterfaces -> einterfaces

* expose public/ submodule

* go mod tidy

* .github: cache-dependency-path, setup-go-work

* modules-tidy for public/ too

* remove old gomodtidy

server/public/model/channel_sidebar_test.go

@@ -0,0 +1,49 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package model
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestIsValidCategoryId(t *testing.T) {
+	for _, test := range []struct {
+		Name     string
+		Input    string
+		Expected bool
+	}{
+		{
+			Name:     "should accept a regular ID",
+			Input:    NewId(),
+			Expected: true,
+		},
+		{
+			Name:     "should accept a favorites ID",
+			Input:    fmt.Sprintf("favorites_%s_%s", NewId(), NewId()),
+			Expected: true,
+		},
+		{
+			Name:     "should accept a channels ID",
+			Input:    fmt.Sprintf("channels_%s_%s", NewId(), NewId()),
+			Expected: true,
+		},
+		{
+			Name:     "should accept a direct messages ID",
+			Input:    fmt.Sprintf("direct_messages_%s_%s", NewId(), NewId()),
+			Expected: true,
+		},
+		{
+			Name:     "should reject a garbage ID",
+			Input:    "a garbage ID",
+			Expected: false,
+		},
+	} {
+		t.Run(test.Name, func(t *testing.T) {
+			assert.Equal(t, test.Expected, IsValidCategoryId(test.Input))
+		})
+	}
+}