[mlir][Complex] Add convenience builder for complex.number attribute.

[pifon2a]

Nice!

[akuegel]

Improve indentation.

mlir/include/mlir/Dialect/Complex/IR/ComplexAttributes.td

let description = [{
     ```mlir
     #complex.number<:f64 1.0, 2.0>
     ```
   }];
 
   let parameters = (ins APFloatParameter<"">:$real,
                         APFloatParameter<"">:$imag,
                         AttributeSelfTypeParameter<"">:$type);
+  let builders = [
+    AttrBuilderWithInferredContext<(ins "mlir::ComplexType":$type, "double":$real, "double":$imag), [{
+      auto elementType = type.getElementType().cast<FloatType>();
+      APFloat realFloat(real);
+      bool unused;
+      realFloat.convert(elementType.getFloatSemantics(),
+                        APFloat::rmNearestTiesToEven, &unused);
+      APFloat imagFloat(imag);
+      imagFloat.convert(elementType.getFloatSemantics(),
+                        APFloat::rmNearestTiesToEven, &unused);
+      return $_get(type.getContext(), realFloat, imagFloat, type);
+    }]>
+  ];
+
   let genVerifyDecl = 1;
   let hasCustomAssemblyFormat = 1;
+  let skipDefaultBuilders = 1;
 }
 
 #endif // COMPLEX_ATTRIBUTE

mlir/lib/Dialect/Complex/IR/ComplexDialect.cpp

 Attribute complex::NumberAttr::parse(AsmParser &parser, Type odsType) {
   Type type;
   double real, imag;
   if (parser.parseLess() || parser.parseColon() || parser.parseType(type) ||
       parser.parseFloat(real) || parser.parseComma() ||
       parser.parseFloat(imag) || parser.parseGreater())
     return {};
 
-  bool unused = false;
-  APFloat realFloat(real);
-  realFloat.convert(type.cast<FloatType>().getFloatSemantics(),
-                    APFloat::rmNearestTiesToEven, &unused);
-  APFloat imagFloat(imag);
-  imagFloat.convert(type.cast<FloatType>().getFloatSemantics(),
-                    APFloat::rmNearestTiesToEven, &unused);
-  return NumberAttr::get(parser.getContext(), realFloat, imagFloat,
-                         ComplexType::get(type));
+  return NumberAttr::get(ComplexType::get(type), real, imag);
 }