Add support for MAXAR_content_geojson 3D Tiles extension

[lilleyse]

Fixes #10320.
Merge #10350 and #10351 first

This PR adds support for the MAXAR_content_geojson 3D Tiles extension which makes it possible to load vector data in the OWT Well Formed Format. This is not a replacement for Vector Tiles which still needs more planning.

There are several constraints on the GeoJSON files:

• The top level GeoJSON type must be FeatureCollection or Feature.
• The geometry types must be LineString, MultiLineString, MultiPolygon, or Polygon.
• All geometries are converted to geodesic lines.
• Only WGS84 geographic coordinates are supported.

2D and 3D coordinates are supported. GeoJSON properties are supported as well. All the features in the GeoJSON are batched into a single primitive to ensure good performance, and feature IDs are generated so that features are still individually pickable and styleable.

Future work:

• Process GeoJSON in Web Worker to avoid hitches
• Triangulate polygons

Local sandcastle for visualizing the test models

[cesium-concierge]

Thanks for the pull request @lilleyse!

• ✔️ Signed CLA found.

Reviewers, don't forget to make sure that:

• Cesium Viewer works.
• Works in 2D/CV.

[IanLilleyT]

I pushed some very small code changes. Otherwise the PR looks great! I tested with a very large dataset and it rendered the lines in the correct places.

[IanLilleyT]

can unload be called before parse? Should it do this._geoJson = undefined; too?

[IanLilleyT]

Never mind, after checking out GltfLoader it does a similar thing to this (unsets the json after loading finishes).