MAXAR_content_geojson tilesets should be more like vector tiles

[timoore]

GeoJSON data in tilesets using the MAXAR_content_geojson are faithfully translated into glTF geometry and structured metadata, but they don't retain the vector qualites of the original data. The new extensions developed for vector tiles should be used with these tilesets:

• 3DTILES_content_gltf_vector indicates that the tile content is vector content;
• KHR_mesh_primitive_restart to preserve line strings in an efficient way;
• EXT_mesh_polygon to preserve topology of polygons, currently lost in the translation to triangles.