ivi-shell: add new signal to notify ivi shell destroying
requested to merge khangtb/weston:ivi_shell_install_compositor_destroy_signal_after_startup_completion into main
In the case the controlelrs are depended on ivi-shell resource, it must be destroy before the ivi shell destroy. To do this, add new ivi shell destroy signal on ivi shell, emit it on the begining of the shell destroying