Migration the stablehlo reduction family of operations, with promotable semantics [RFC](https://github.com/openxla/stablehlo/pull/1664), to MHLO.

Migration the stablehlo reduction family of operations, with promotable semantics [RFC](https://github.com/openxla/stablehlo/pull/1664), to MHLO. #26552