Error estimation with libCEED operators

[sebastiangrimberg]

We can make use of the libCEED partial assembly decomposition to accelerate error estimation quite a bit, at least to perform the interpolation of the smooth and coarse flux fields at quadrature points. This currently involves recomputing a lot of quantities we already have access to, including the element Jacobians and other geometry data.

This would also enable error estimation to take place fully on the GPU.