Add closure attribute option

[1ec5]

The Directions API added a closure option to the annotations query parameter and a corresponding closure property to the per-leg annotation object in 2019. We should add a closure case to AttributeOptions and a closures property to RouteLeg.Attributes. It shouldn’t be called segmentClosures: this annotation type is different from the others in that the array contains a list of closures, similar to the incidents array, rather than one element per leg segment.

/ref #164 mapbox/mapbox-java#1251
/cc @mandeepsandhu