Change the formatting of parameters that are function types. #3671

Related to this PR #3670
All function type parameters are currently in the format of <return-type> <name><type-parameters>()

For example, for source code of:

Object? extractIterableTypeArgument(
        Iterable iterable, Object? Function<T>() extract) =>
    internal.extractTypeArguments<Iterable>(iterable, extract);

Dartdoc renders it as:

extractIterableTypeArgument(Iterable iterable, Object? extract<T>()) → Object?

Object? extract<T>() instead of Object? Function<T>() extract

So perhaps change the format to one of the following

• Always display the new format.
• Always display what is in the source code; if they wrote the old school format, support that. There are plenty of cases in the Dart SDK at least that use the old school format, like Future.then.