A11y: the Showing state is used only for windows
The Showing At-SPI state is set only for anything which has the window role. I don't whether the decision was deliberate, but it at least broke Orca, namely at least in orca#267 (comment 1555378). Maybe the Showing state should be added to the already present Visible one? Or should Orca stop relying on both of these being present?