split(data/{finset,set}/pointwise): Split off `algebra.pointwise` (#12831)
Split `algebra.pointwise` into
* `data.set.pointwise`: Pointwise operations on `set`
* `data.finset.pointwise`: Pointwise operations on `finset`
I'm crediting
* The same people for `data.set.pointwise`
* Floris for #3541