chore(data/set/finite): use dot notation (#3151)
Rename:
* `finite_insert` to `finite.insert`;
* `finite_union` to `finite.union`;
* `finite_subset` to `finite.subset`;
* `finite_image` to `finite.image`;
* `finite_dependent_image` to `finite.dependent_image`;
* `finite_map` to `finite.map`;
* `finite_image_iff_on` to `finite_image_iff`;
* `finite_preimage` to `finite.preimage`;
* `finite_sUnion` to `finite.sUnion`;
* `finite_bUnion` to `finite.bUnion`, merge with `finite_bUnion'` and
use `f : Π i ∈ s, set α` instead of `f : ι → set α`;
* `finite_prod` to `finite.prod`;
* `finite_seq` to `finite.seq`;
* `finite_subsets_of_finite` to `finite.finite_subsets`;
* `bdd_above_finite` to `finite.bdd_above`;
* `bdd_above_finite_union` to `finite.bdd_above_bUnion`;
* `bdd_below_finite` to `finite.bdd_below`;
* `bdd_below_finite_union` to `finite.bdd_below_bUnion`.
Delete
* `finite_of_finite_image_on`, was a copy of `finite_of_fintie_image`;
* `finite_bUnion'`: merge with `finite_bUnion` into `finite.bUnion`.
