AtPoints Operator Rebuild API

[jeremylt]

For our AtPoints CeedOperators, we really should have an API to rebuild the operator from new CeedRestrictions. For a CPU backend it will likely just be cheaper to destroy and recreate the operator with new AtPoints restrictions, but for the GPU we could save a fair amount of JiT time this way.

The API could look something like this:

CeedOperatorAtPointsRebuild(op_old, at_points_rstr_new, *op_new)

CeedOperatorCompositeAtPointsRebuild(op_old, *at_points_rstrs_new, *op_new)