build
fun buildCasing(zoom: Int, properties: Map<String, Any?> = emptyMap(), featureState: Map<String, Any?>? = null, geometryType: MvtGeometryType? = null): ShapeAttributes?
Resolve the casing-stroke ShapeAttributes for one feature. Returns null if this rule has no casing paint. The result is meant to be emitted as a SEPARATE line shape at a slightly lower z-order than build's result, so the wider casing paints underneath the narrower fill.