Add a debugShowBoundingSpheres option to Cesium3DTileset?

[ptrgags]

When working on ModelExpeirimental, often I want to see not just the tile bounding volumes, but the draw command bounding volumes for debugging purposes.

For individual models, this can be done with the debugShowBoundingVolume option, which just sets the same property on each DrawCommand

For 3D Tiles, we already have tileset.debugShowBoundingVolume, but adding a debugShowBoundingSpheres or debugShowDrawCommandBounds option might be helpful here. Though this would require updating every type of Cesium3DTileContent.

Another option is to only support this flag for tilesets that use ModelExperimental for now (and mark it as an experimental parameter)

Any thoughts @sanjeetsuhag @lilleyse?

[sanjeetsuhag]

@ptrgags I like this suggestion and it has been something I find lacking in the current API too. In terms of naming, maybe could use showBoundingVolume and showPrimitiveBoundingVolumes.

[ptrgags]

I don't think showPrimitiveBoundingVolumes is a great idea, as it may cause confusion with the Primitive interface (and Cesium3DTileset implements this interface). From a user perspective, "primitive" means anything renderable, not glTF primitive.