Function clear_signal_dirty 

pub fn clear_signal_dirty(signals: Option<ResMut<'_, Signals>>)

Clears the legacy Signals::dirty set at the end of crate::tick::TickStage::A11ySync. Argument is Option<ResMut<Signals>> so the system no-ops when the Signals resource is absent. Post wave-D the canonical dirty queue lives on PropertyStore and is cleared by crate::property_store::clear_property_store_dirty.