chore(data/equiv): split and move to `logic/equiv` (#12929)
Zulip discussion: https://leanprover.zulipchat.com/#narrow/stream/113488-general/topic/Rearranging.20files.20in.20.60data.2F.60
This PR rearranges files in `data/equiv/` by 1) moving bundled isomorphisms to a relevant subfolder of `algebra/`; 2) moving `denumerable` and `encodable` to `logic/`; 3) moving the remainder of `data/equiv/` to `logic/equiv/`. The commits of this PR correspond to those steps.
In particular, the following files were moved:
* `data/equiv/module.lean` → `algebra/module/equiv.lean`
* `data/equiv/mul_add.lean` → `algebra/hom/equiv.lean`
* `data/equiv/mul_add_aut.lean` → `algebra/hom/aut.lean`
* `data/equiv/ring.lean` → `algebra/ring/equiv.lean`
* `data/equiv/ring_aut.lean` → `algebra/ring/aut.lean`
* `data/equiv/denumerable.lean` → `logic/denumerable.lean`
* `data/equiv/encodable/*.lean` → `logic/encodable/basic.lean logic/encodable/lattice.lean logic/encodable/small.lean`
* `data/equiv/*.lean` to: `logic/equiv/basic.lean logic/equiv/fin.lean logic/equiv/functor.lean logic/equiv/local_equiv.lean logic/equiv/option.lean logic/equiv/transfer_instance.lean logic/equiv/embedding.lean logic/equiv/fintype.lean logic/equiv/list.lean logic/equiv/nat.lean logic/equiv/set.lean`
