Support polygons with holes

[kylebarron]

The SolidPolygonLayer mentions holeIndices, but it's not clear if that works with binary attributes as well.

[kylebarron]

For the record, it doesn't seem to crash on polygons with holes... it just renders the hole as well

[kylebarron]

Felix mentioned that the MVTLayer currently renders polygons with holes via the indices attribute.

https://github.com/visgl/deck.gl/blob/6e6b48b82aa498b957ac775db15e62523c0c6e45/modules/layers/src/geojson-layer/geojson-layer-props.ts#L123-L125

See also the triangles attribute in the output of geojsonToBinary: https://loaders.gl/docs/modules/gis/api-reference/geojson-to-binary#outputs

[kylebarron]

https://github.com/visgl/loaders.gl/blob/a52ce43b3a5dd3461344398f13de3efe4d93e684/modules/gis/src/lib/flat-geojson-to-binary.ts#L446-L453

Ok so things to note here:

• hole coordinates are offset by the start index of the polygon
• In the short run, just slice/view the coordinates array, update the offsets of the geom_offsets array, and update the indices after you're done.
• Use math.gl/polygon, which is updated to use typed arrays.
• It's interesting that the output size is 1, not 3 for the triangles.
• In the long run, we should implement earcut to use indices on an existing coordinate array. This has the potential to be extremely fast.
• Or... eventually explore earcut from rust.