Moving slash-commands out of app package (#14979)

* Moving slash-commands out of app package

* Fixing golint checks

* Fixing golangci-lint

* Fixing golangci-lint errors

app/slashcommands/command_code.go

@@ -0,0 +1,45 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package slashcommands
+
+import (
+	"strings"
+
+	goi18n "github.com/mattermost/go-i18n/i18n"
+	"github.com/mattermost/mattermost-server/v5/app"
+	"github.com/mattermost/mattermost-server/v5/model"
+)
+
+type CodeProvider struct {
+}
+
+const (
+	CMD_CODE = "code"
+)
+
+func init() {
+	app.RegisterCommandProvider(&CodeProvider{})
+}
+
+func (me *CodeProvider) GetTrigger() string {
+	return CMD_CODE
+}
+
+func (me *CodeProvider) GetCommand(a *app.App, T goi18n.TranslateFunc) *model.Command {
+	return &model.Command{
+		Trigger:          CMD_CODE,
+		AutoComplete:     true,
+		AutoCompleteDesc: T("api.command_code.desc"),
+		AutoCompleteHint: T("api.command_code.hint"),
+		DisplayName:      T("api.command_code.name"),
+	}
+}
+
+func (me *CodeProvider) DoCommand(a *app.App, args *model.CommandArgs, message string) *model.CommandResponse {
+	if len(message) == 0 {
+		return &model.CommandResponse{Text: args.T("api.command_code.message.app_error"), ResponseType: model.COMMAND_RESPONSE_TYPE_EPHEMERAL}
+	}
+	rmsg := "    " + strings.Join(strings.Split(message, "\n"), "\n    ")
+	return &model.CommandResponse{ResponseType: model.COMMAND_RESPONSE_TYPE_IN_CHANNEL, Text: rmsg, SkipSlackParsing: true}
+}