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/client.go

@@ -0,0 +1,54 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package plugin
+
+import (
+	"github.com/hashicorp/go-plugin"
+)
+
+const (
+	InternalKeyPrefix = "mmi_"
+	BotUserKey        = InternalKeyPrefix + "botid"
+)
+
+// Starts the serving of a Mattermost plugin over net/rpc. gRPC is not yet supported.
+//
+// Call this when your plugin is ready to start.
+func ClientMain(pluginImplementation any) {
+	if impl, ok := pluginImplementation.(interface {
+		SetAPI(api API)
+		SetDriver(driver Driver)
+	}); !ok {
+		panic("Plugin implementation given must embed plugin.MattermostPlugin")
+	} else {
+		impl.SetAPI(nil)
+		impl.SetDriver(nil)
+	}
+
+	pluginMap := map[string]plugin.Plugin{
+		"hooks": &hooksPlugin{hooks: pluginImplementation},
+	}
+
+	plugin.Serve(&plugin.ServeConfig{
+		HandshakeConfig: handshake,
+		Plugins:         pluginMap,
+	})
+}
+
+type MattermostPlugin struct {
+	// API exposes the plugin api, and becomes available just prior to the OnActive hook.
+	API    API
+	Driver Driver
+}
+
+// SetAPI persists the given API interface to the plugin. It is invoked just prior to the
+// OnActivate hook, exposing the API for use by the plugin.
+func (p *MattermostPlugin) SetAPI(api API) {
+	p.API = api
+}
+
+// SetDriver sets the RPC client implementation to talk with the server.
+func (p *MattermostPlugin) SetDriver(driver Driver) {
+	p.Driver = driver
+}