Add rewrite pattern into AggresiveSimplification that turns compare+select into min/max

[mvpant]

This patch rewrites a comparison and selection combination that utilizes the same operands into a min/max operation:

func.func @test(%arg0: tensor<2xi32>, %arg1: tensor<2xi32>) -> (tensor<2xi32>, tensor<2xi32>) {
  %0 = stablehlo.compare GE, %arg0, %arg1, SIGNED : (tensor<2xi32>, tensor<2xi32>) -> tensor<2xi1>
  %1 = stablehlo.compare LE, %arg0, %arg1, SIGNED : (tensor<2xi32>, tensor<2xi32>) -> tensor<2xi1>
  %s0 = stablehlo.select %0, %arg0, %arg1 : (tensor<2xi1>, tensor<2xi32>, tensor<2xi32>) -> tensor<2xi32>
  %s1 = stablehlo.select %1, %arg0, %arg1 : (tensor<2xi1>, tensor<2xi32>, tensor<2xi32>) -> tensor<2xi32>
  return %s0, %s1 : tensor<2xi32>, tensor<2xi32>
}

transformed into:

func.func @test(%arg0: tensor<2xi32>, %arg1: tensor<2xi32>) -> (tensor<2xi32>, tensor<2xi32>) {
  %0 = stablehlo.maximum %arg0, %arg1 : tensor<2xi32>
  %1 = stablehlo.minimum %arg0, %arg1 : tensor<2xi32>
  return %0, %1 : tensor<2xi32>, tensor<2xi32>
}

[mvpant]

I am primarily interested in implementing this simplification within the reduce body. Should I restrict the scope of the pattern?

[mlevesquedion]

Looks great! No need to restrict to reduce, I think this is good to have everywhere.

Just a few nits, PTAL.