chore(topology/algebra/uniform_mul_action): add `has_uniform_continuous_const_smul.op` (#12434)
chore(topology/algebra/uniform_mul_action): add `has_uniform_continuous_const_smul.op` (#12434)

This matches `has_continuous_const_smul.op` and other similar lemmas.

With this in place, we can state `is_central_scalar` on `completion`s.





leanprover-community/mathlib,leanprover-community/mathlib