chore(*): add mathlib4 synchronization comments (#18490)
Regenerated from the [port status wiki page](https://github.com/leanprover-community/mathlib/wiki/mathlib4-port-status).
Relates to the following files:
* `category_theory.bicategory.End`
* `category_theory.essentially_small`
* `category_theory.functor.epi_mono`
* `category_theory.functor.reflects_isomorphisms`
* `category_theory.monoidal.functor`
* `data.qpf.multivariate.constructions.fix`
* `dynamics.flow`
* `group_theory.noncomm_pi_coprod`
* `linear_algebra.linear_independent`
* `set_theory.cardinal.ordinal`
