Add support for reprojecting from HiPS and HiPS3D to standard projections

The easiest approach might be to use https://github.com/astropy/reproject/pull/514 and pass that to e.g. ``reproject_interp`` - we could make a wrapper for it though. Need to make sure I understand the performance implications of passing a potentially huge dask array to ``reproject_interp`` - we won't be able to dump that to a memory map.

Start by reviewing astropy/reproject#514 and the proposed use of reproject_interp. Investigate the performance implications of passing a potentially huge dask array without using a memory map, then define a wrapper that supports reprojecting HiPS and HiPS3D data to standard projections.

Written by the indexing model from the issue text.