feat(topology/maps): more `iff` lemmas (#15165)
* add `inducing_iff` and `inducing_iff_nhds`;
* add `embedding_iff`;
* add `open_embedding_iff_embedding_open` and `open_embedding_iff_continuous_injective_open`;
* add `open_embedding.is_open_map_iff`;
* reorder `open_embedding_iff_open_embedding_compose` and `open_embedding_of_open_embedding_compose`, golf.
