build
fun buildIcon(zoom: Int, properties: Map<String, Any?>, featureState: Map<String, Any?>? = null, geometryType: MvtGeometryType? = null): MvtStyleRule.IconSpec?
Resolve this rule's icon paint for one feature. Returns null when iconImage is unset, or when the resolved icon name (after {property} substitution) is empty. Caller is responsible for looking up the name in an MvtSpriteAtlas.