make S3 methods for grid functions that dispatch from model/recipe/workflow

[topepo]

To eliminate a step of extracting the parameter set and for future-proofing for mixed grids (where we need to know about submodel parameters).

[hfrick]

So grid_random.recipe() or grid_space_filling.workflow()? Since we generally try to stick S3 methods for a class into the same package as the class itself, should we open issues for this on recipes/parsnip/workflows?