Add support for Null / Default or const values on Parameters

# Description

It's not at all uncommon to have constructor or method parameters that are optional with `default`, `null` or constant values like:

```cs
public Task DoSomethingAsync(string name = null, int interval = 5, CancellationToken = default)
{
}
```

The add parameter methods should be redone to support these various ways of providing a default value for optional parameters.