chore(*): add mathlib4 synchronization comments (#19214)
Regenerated from the [port status wiki page](https://github.com/leanprover-community/mathlib/wiki/mathlib4-port-status).
Relates to the following files:
* `algebraic_geometry.presheafed_space.gluing`
* `analysis.calculus.bump_function_findim`
* `field_theory.polynomial_galois_group`
* `geometry.manifold.sheaf.basic`
* `linear_algebra.clifford_algebra.conjugation`
* `linear_algebra.clifford_algebra.grading`
* `linear_algebra.clifford_algebra.star`
* `linear_algebra.free_module.norm`
* `number_theory.cyclotomic.discriminant`
* `number_theory.legendre_symbol.add_character`
* `number_theory.number_field.canonical_embedding`
