Send ObjectShow event for visible components after initialized

Currently ObjectShow event is only sent when the visible property changes from false to true, but for items with the notification accessible role, a screen reader like Orca needs to receive an ObjectShow event to read the notification, so also send the event after a component is initialized.

See also: https://gitlab.gnome.org/GNOME/orca/-/merge_requests/134

Pick-to: 6.4 Change-Id: I626594b65ffe4d0582dcee9f489df0c2c63e53b7 Reviewed-by: Jan Arve Sæther jan-arve.saether@qt.io (cherry picked from commit 9a4f2d23)

Build log: https://build.opensuse.org/package/live_build_log/home:fusionfuture:branches:KDE:Qt:5.15/libqt5-qtdeclarative/openSUSE_Tumbleweed/x86_64

Ref: plasma/plasma-desktop#41 (closed)