Default Uri constructors brings a lot of dependencies

Using a simple program like

```c#
using System;

class Program
{
    static void Main(string[] args)
    {
        Console.WriteLine(new Uri ("www.microsoft.com"));
    }
}
```

shows that the default Uri constructor brings a lot for size-optimized setup. The size increase for adding Uri constructor is about 80 KB which seems to be a lot for a simple "default" constructor call.