Have a single compute function register multiple variables

[unalmis]

Requested by @ddudt

Could be nice to generalize the register_compute_fun decorator for multiple names and multiple descriptions for compute functions that compute multiple stuff. My suggestion would be to check if name and description is a list and then loop through to register them in compute.utils/data_index.py.

Note that this would be a cosmetic change to remove duplicate code. We already ensure computation is not performed when something is already computed.

• curvature1, curvature2
• theta_B, zeta_B

[ddudt]

This was not really resolved by #1166. We came up with a hack for the two cases that exist in the current code. Is that solution our plan going forward for all similar instances? Or do we still want to add special logic to handle this?