chore(algebra/ring): move `add_mul_self_eq` to `comm_semiring` (#3089)
chore(algebra/ring): move `add_mul_self_eq` to `comm_semiring` (#3089)

Also use `alias` instead of `def ... := @...` to make linter happy.

Fixes https://github.com/leanprover-community/lean/issues/232





leanprover-community/mathlib,leanprover-community/mathlib