Ortho-slicing for 3d Chunked Data

[ilan-gold]

Starting this as a way of looking at the data here: hms-dbmi/vizarr#103 (comment) so it doesn't get lost in the sauce

Not really sure how we'd formalize the API for this - we really need two things

1. A way of telling the MultiscaleImageLayer to re-calculate the z-selection (or whichever axis you are selecting along) based on image pyramid size and resolution
2. A way of informing the loader to invert the selection so you can get chunks along a different axis

Less pressingly we would need to allow non quintuples for axis labels/shape.

This PR is in a very hacky state such that it only works with the dataset from the linked issue. To change the axis you select on you'll need to change the "selection order" so

• the returned image size for padding
• the ordering for the shape
• as well as the selection mechanism in both getRaster and getTile

This is where the API would be need to be carefully designed, some sort of prop or the like would need to be added.