Broadcast application menu on PWM interface initiaization

Summary:
By the time AbstractClient::setupWindowManagementInterface() is called,
it's possible for a window to already have an application menu, and not update them
afterwards.

Reviewers: #kwin, zzag

Reviewed By: #kwin, zzag

Subscribers: kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D28150

abstract_client.cpp

@@ -1364,6 +1364,7 @@ void AbstractClient::setupWindowManagementInterface()
     w->setMaximizeable(isMaximizable());
     w->setMinimizeable(isMinimizable());
     w->setFullscreenable(isFullScreenable());
+    w->setApplicationMenuPaths(applicationMenuServiceName(), applicationMenuObjectPath());
     w->setIcon(icon());
     auto updateAppId = [this, w] {
         w->setAppId(QString::fromUtf8(m_desktopFileName.isEmpty() ? resourceClass() : m_desktopFileName));