Since #23940 we have a reasonably good implementation of logarithms for (finite) AdditiveAbelianGroupWrappers, but the method is still named _discrete_log and therefore hidden from the public.

This patch removes the leading underscore. While I was at it, I also removed the underscore from discrete_exp and did a couple smaller things to improve the documentation of that class in general, so that it hopefully looks a little bit less like an obscure internal helper class.

CC: @roed314 @loefflerd

Component: group theory

Keywords: abelian group wrapper, visibility

Author: Lorenz Panny

Branch/Commit: 294f5bd

Reviewer: Vincent Delecroix

Issue created by migration from https://trac.sagemath.org/ticket/32384