[js_interop] Support renaming of parameters in constructors

[fuzzybinary]

Dart currently supports renaming properties in an extension type by doing the following:

extension type TestObject._(JSObject _) {
  @JS('property')
  external String prop;
}

However, it is not possible to rename these same properties during construction of the type, especially anonymous types. For example, the following does not work:

extension type TestObject._(JSObject _) {
  @JS('property')
  external String prop;

  external factory TestObject({
    @JS('property') required String,
  });

The a workaround for this is to either leave the names of parameters in the constructor, or to assign the properties in the body of a factory constructor, but having constructor parameter name renaming would be a much cleaner solution.

[srujzs]

Agreed. Assigning the properties in the body of the constructor leads to different semantics as well because you can't tell in Dart if the value was passed or not (unless you treat null as the sentinel).