chore(*): add mathlib4 synchronization comments (#18342)
Regenerated from the [port status wiki page](https://github.com/leanprover-community/mathlib/wiki/mathlib4-port-status).
Relates to the following files:
* `algebra.big_operators.associated`
* `data.W.constructions`
* `data.dlist.instances`
* `data.multiset.functor`
* `data.sign`
* `data.sum.interval`
* `group_theory.coset`
* `topology.algebra.order.left_right`
* `topology.constructions`
* `topology.continuous_on`
* `topology.inseparable`
* `topology.local_extr`
* `topology.maps`
* `topology.order`
