Activator.CreateInstance remarks outdated

The remarks section of `Activator.CreateInstance()` currently states this:

> In general, there is no use for the `CreateInstance()` generic method in application code, because the type must be known at compile time. If the type is known at compile time, normal instantiation syntax can be used (`new` operator in C#, `New` in Visual Basic, `gcnew` in C++).

This is not correct any more. Consider the following example:

```cs
public class MyType
{
public required string Name { get; set; }
}

public static class MyFactory
{
public static T CreateWithNewConstraint() where T : new()
{
return new T();
}

public static T CreateWithActivator()
{
return Activator.CreateInstance();
}
}

public static class MySample
{
public static void Sample()
{
// This shows compiler error CS9040
var o1 = MyFactory.CreateWithNewConstraint();

// This works fine
var o2 = MyFactory.CreateWithActivator();
}
}
```

Compiler error CS9040 is currently not documented. It has the following message: "'MyType' cannot satisfy the 'new()' constraint on parameter 'T' in the generic type or or method 'MyFactory.CreateWithNewConstraint()' because 'MyType' has required members."