Query tilesets by bounding volume at a particular LOD

[kring]

Tileset::updateView effectively allows you to query for a set of tiles that meets a particular screen-space error from the viewpoint of a camera with a particular perspective frustum. After #1125, this will be extended to multiple independent views. And after #1135, it will be extended to orthographic views.

It would be useful to further extend this idea to allow querying of a set of tiles within a particular bounding box or sphere at a particular level-of-detail.

More generally, we should make it easy for users to implement these kinds of queries external to the Tileset, while still leveraging the progressive loading that Tileset does for views and height queries.

CC @Lee-Bull