New method: is_within_distance

[asinghvi17]

With SpatialTreeInterface, this only needs rect-rect distance to work:

import GeometryOps.SpatialTreeInterface as STI

function foreach_within_distance(f, query_geom_or_rect, tree, geoms, distance) # only planar for now
    STI.do_query((e1) -> rect_rect_distance(e1, GI.extent(query_geom_or_rect)) <= distance, GI.extent(query_geom_or_rect)) do i
        if GO.distance(query_geom_or_rect, geoms[i]) <= distance
            f(geoms[i])
        end
    end
end

function rect_rect_distance(rect1::Extent, rect2::Extent)
    # do something here efficiently
end

But we need a nice structure to keep geometries together with a tree...maybe IndexedGeometry or GeoAcceleratedArray?

We may also need to build a spatial index if one doesn't exist.

Unfortunately, finding the nearest geometry is not so trivial, likely needing an expanding search and some form of stack rejection. We might need a priority queue for that.