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/message_export.go

@@ -0,0 +1,50 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package model
+
+import "encoding/json"
+
+type MessageExport struct {
+	TeamId          *string
+	TeamName        *string
+	TeamDisplayName *string
+
+	ChannelId          *string
+	ChannelName        *string
+	ChannelDisplayName *string
+	ChannelType        *ChannelType
+
+	UserId    *string
+	UserEmail *string
+	Username  *string
+	IsBot     bool
+
+	PostId         *string
+	PostCreateAt   *int64
+	PostUpdateAt   *int64
+	PostDeleteAt   *int64
+	PostMessage    *string
+	PostType       *string
+	PostRootId     *string
+	PostProps      *string
+	PostOriginalId *string
+	PostFileIds    StringArray
+}
+
+type MessageExportCursor struct {
+	LastPostUpdateAt int64
+	LastPostId       string
+}
+
+// PreviewID returns the value of the post's previewed_post prop, if present, or an empty string.
+func (m *MessageExport) PreviewID() string {
+	var previewID string
+	props := map[string]any{}
+	if m.PostProps != nil && json.Unmarshal([]byte(*m.PostProps), &props) == nil {
+		if val, ok := props[PostPropsPreviewedPost]; ok {
+			previewID = val.(string)
+		}
+	}
+	return previewID
+}