feat(algebra/order_functions): define `min/max_mul_of_nonneg` (#1698)
feat(algebra/order_functions): define `min/max_mul_of_nonneg` (#1698)

Also define `monotone_mul_right_of_nonneg` and rename
`monotone_mul_of_nonneg` to `monotone_mul_left_of_nonneg`.
leanprover-community/mathlib,leanprover-community/mathlib