chore(data/{equiv,set}/basic): image_preimage (#5465)
* `equiv.symm_image_image`: add `@[simp]`;
* `equiv.image_preimage`, `equiv.preimage_image`: new `simp` lemmas;
* `set.image_preimage_eq`, `set.preimage_image_eq`: make `s : set _` an explicit argument;
* `function.injective.preimage_image`, `function.surjective.image_preimage`: new aliases for `set.preimage_image_eq`
and `set.image_preimage_eq` with arguments reversed
Also golf a proof about `separated`.
