chore(*): add mathlib4 synchronization comments (#18642)
Regenerated from the [port status wiki page](https://github.com/leanprover-community/mathlib/wiki/mathlib4-port-status).
Relates to the following files:
* `algebra.char_p.algebra`
* `analysis.normed_space.M_structure`
* `category_theory.groupoid.vertex_group`
* `category_theory.limits.shapes.multiequalizer`
* `category_theory.limits.shapes.reflexive`
* `combinatorics.derangements.basic`
* `combinatorics.simple_graph.degree_sum`
* `data.polynomial.denoms_clearable`
* `data.polynomial.ring_division`
* `data.set.sups`
* `linear_algebra.affine_space.affine_equiv`
* `number_theory.pythagorean_triples`
* `number_theory.zsqrtd.basic`
* `number_theory.zsqrtd.to_real`
* `ring_theory.localization.num_denom`
* `topology.path_connected`
