WIP add quantized mesh loader to terrain layer

[kylebarron]

Background

The Quantized Mesh loader was added in loaders.gl 2.2, which parses the Quantized Mesh format.

Change List

• Add QuantizedMeshLoader to the loaders list when loading terrain

Notes

Web Mercator Projection only

Quantized Mesh is often tiled in the EPSG: 4326 projection, which is incompatible with the current TileLayer, which only accepts Web Mercator/OSM indexing.

Mesh orientation

This is an issue I've struggled with before. Without changing the existing code when I use quantized mesh I see the images flipped:

I might need to check that I'm serving the mesh according to the spec

cc @davidbrochart, #4531

[coveralls]

Coverage decreased (-0.08%) to 83.529% when pulling 45ab2b9 on kyle/quantized-mesh-terrain-layer into 76085c7 on master.

[Pessimistress]

To avoid overbundling dependencies and be more future proof, this layer could adopt the Tile3DLayer's loader approach. The default loader would be the terrain loader, but users can choose to import another.

Similarly, rather than hardcoding format-specific logic, loaders should come up with a schema that describes the mesh coordinate system/transform in the returned header, for this layer to consume.

[Pessimistress]

The use of CARTESIAN coordinates in this layer should not be mandatory. It is an optimization for rendering a specific format (color-coded image) to a specific projection (Web Mercator). If we want this layer to support e.g. globe view, the loader will have to provide the option to output wgs84 coordinates.