New <leaflet-icon> element wraps L.Icon / L.DivIcon and dispatches
icon-changed custom events to parent markers. Marker listens for
the event and queries for existing icon children on connect.
Fix: use kebab-case attribute names (via PROPS table spec.attr) in
applyIcon() instead of camelCase, and guard against empty iconUrl
to avoid L.icon({}) throwing.
Buddy