build
fun buildText(zoom: Int, properties: Map<String, Any?>, featureState: Map<String, Any?>? = null, geometryType: MvtGeometryType? = null): MvtStyleRule.LabelSpec?
Resolve the label text + TextAttributes for one feature. Returns null if this rule isn't a text rule (hasText is false), or if the feature has no value for textField, or the value's string form is empty.
The text is properties[textField].toString().trim() — MVT property values can arrive as String / Long / Double / Boolean, all of which have sensible string forms for label use.