message: Make DotDimensionNumbers more specific.
  This makes client code easier to write.
diff: @@ -944,10 +944,11 @@ def HLO_DotOp: HLO_Op<"dot", [NoSideEffect]>, BASE_HLO_DotOp {
  }
  def DotDimensionNumbers : StructAttr<"DotDimensionNumbers", HLO_Dialect, [
  - StructFieldAttr<"lhs_batching_dimensions", ElementsAttr>,
  - StructFieldAttr<"rhs_batching_dimensions", ElementsAttr>,
  - StructFieldAttr<"lhs_contracting_dimensions", ElementsAttr>,
  - StructFieldAttr<"rhs_contracting_dimensions", ElementsAttr>] > {
  + StructFieldAttr<"lhs_batching_dimensions", I64ElementsAttr>,
  + StructFieldAttr<"rhs_batching_dimensions", I64ElementsAttr>,
  + StructFieldAttr<"lhs_contracting_dimensions", I64ElementsAttr>,
  + StructFieldAttr<"rhs_contracting_dimensions", I64ElementsAttr>
  + ]> {
  let description = "Structure of dimension information for dot product";
  }
  