chore(*): add mathlib4 synchronization comments (#18646)
Regenerated from the [port status wiki page](https://github.com/leanprover-community/mathlib/wiki/mathlib4-port-status).
Relates to the following files:
* `algebra.category.Group.basic`
* `algebra.star.free`
* `analysis.convex.segment`
* `analysis.convex.star`
* `category_theory.concrete_category.elementwise`
* `category_theory.limits.concrete_category`
* `category_theory.limits.shapes.diagonal`
* `category_theory.limits.shapes.types`
* `category_theory.localization.construction`
* `category_theory.monad.basic`
* `category_theory.monoidal.natural_transformation`
* `category_theory.morphism_property`
* `category_theory.sites.grothendieck`
* `data.finset.sym`
* `data.mv_polynomial.equiv`
* `data.polynomial.field_division`
* `group_theory.free_product`
* `information_theory.hamming`
* `linear_algebra.affine_space.affine_subspace`
* `linear_algebra.affine_space.midpoint`
* `linear_algebra.affine_space.restrict`
* `number_theory.fermat4`
* `number_theory.padics.padic_norm`
* `ring_theory.polynomial.content`
