update_reparented performs an O(n) table scan over all entities with parents #23155
Description
Problem
update_reparented performs a change detection scan over every entity with a ChildOf component.
This is slow at high entity count!
On 0.18 update_reparented has a pretty gnarly perf issue. I have almost no ui, but I am paying 8ms every frame to run that system because I have 4m entities.
system{name="bevy_app::propagate::update_reparented<bevy_ui::ui_node::ComputedUiTargetCamera, (), bevy_ecs::hierarchy::ChildOf>"}
system{name="bevy_app::propagate::update_reparented<bevy_ui::ui_node::ComputedUiRenderTargetInfo, (), bevy_ecs::hierarchy::ChildOf>"}