chore(data/set/finite): rename some lemmas (#7241)
### Revert some name changes from #5813
* `set.fintype_set_bUnion` → `set.fintype_bUnion`;
* `set.fintype_set_bUnion'` → `set.fintype_bUnion'`;
* `set.fintype_bUnion` → `set.fintype_bind`;
* `set.fintype_bUnion'` → `set.fintype_bind'`;
* `set.finite_bUnion` → `set.finite.bind`;
### Add a few lemmas
* `set.finite_Union_Prop`;
* add `set.seq` versions of lemmas/defs about `<*>` (they work for `α`, `β` in different universes).
