feat(algebra/ring): mark a useful lemma simp and generalize unit neg lemmas (#16993)
feat(algebra/ring): mark a useful lemma simp and generalize unit neg lemmas (#16993)

Mark the lemma that states `is_unit (-x) \iff is_unit x` as `simp`, and while we are here generalize a couple of typeclasses to a general monoid with some distributive negation.





leanprover-community/mathlib,leanprover-community/mathlib