refactor(topology/algebra): reorder imports (#12089)
* move `mul_opposite.topological_space` and `units.topological_space` to a new file;
* import `mul_action` in `monoid`, not vice versa.
With this order of imports, we can reuse results about `has_continuous_smul` in lemmas about topological monoids.
Co-authored-by: Eric Wieser <wieser.eric@gmail.com>
