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/plugin/product.go

@@ -0,0 +1,41 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package plugin
+
+import (
+	"net/http"
+)
+
+type RegisteredProduct struct {
+	ProductID string
+	Adapter   Hooks
+}
+
+func (rp *RegisteredProduct) Implements(hookId int) bool {
+	adapter, ok := rp.Adapter.(*HooksAdapter)
+	if !ok {
+		return false
+	}
+
+	_, ok = adapter.implemented[hookId]
+	return ok
+}
+
+// Implemented method is overridden intentionally to prevent calling it from outside.
+func (a *HooksAdapter) Implemented() ([]string, error) {
+	return nil, nil
+}
+
+// OnActivate is overridden intentionally as product should not call it.
+func (a *HooksAdapter) OnActivate() error {
+	return nil
+}
+
+// OnDeactivate is overridden intentionally as product should not call it.
+func (a *HooksAdapter) OnDeactivate() error {
+	return nil
+}
+
+// ServeHTTP is overridden intentionally as product should not call it.
+func (a *HooksAdapter) ServeHTTP(c *Context, w http.ResponseWriter, r *http.Request) {}