Add support for reprojecting from HiPS and HiPS3D to standard projections

[astrofrog]

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.