REF: standardize usage in DataFrame vs SparseDataFrame ops
I _think_ that after this we're not far from being able to use the base class versions of _combine_frame, _combine_match_index, _combine_match_columns, and _combine_const.  That'll be a good day.

The only actual behavior changed is in SparseDataFrame._combine_match_columns, which is changed to match the other methods.  See #28025 