Broadcast application menu to resources when registering them

Summary:
Previously, KWayland wasn't hanging onto the application menu
to broadcast it when registering a resource. This fixes that.

Reviewers: KWin, zzag

Reviewed By: KWin, zzag

Subscribers: kde-frameworks-devel, zzag

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D28168