Fix composites failing when inputs are different chunk sizes

[djhoese]

While working on using the CREFL rayleigh correction on MODIS data I noticed a couple issues. This PR fixes:

1. The variable name was incorrect for the DEM file typically used with MODIS data (tbase.hdf)
2. The tbase.hdf file doesn't have a fill value specified so it was causing the code to fail when reading it.
3. Any composites that use map_blocks or blockwise will fail if they have different chunk sizes for their inputs. This is happening for MODIS data due to the angle datasets being returned as 64-bit floats when they only need to be 32-bit floats (that'll be another PR). Anyway, I've added a unify_chunks method that is automatically run as part of match_data_arrays that all Composites typically follow.

• Tests added

[djhoese]

🤦‍♂️ I already made #1808 which includes these commits. Let me redo this.