Batch version of curl

Description

The batch curl version assumes that the components in the states of the batch are the different spatial dimensions of the functions. It only works for 3D meshes. The batch can contain several vectors; the curl will then be computed for each of them.

For non-orthogonal meshes, it assumes that the vector components of the function (i.e. the values in the batch) are given in Cartesian coordinates, so they are not transformed.

Depends on !743 (merged).

News snippet

Batch version of curl.

Checklist

• I have checked that my code follows the Octopus coding standards
• I have added tests for all the new features added in this request.