Allow generic and nested types in x:DataType and x:Type

[BaY1251]

Support compiled bindings for ViewModels based on a generic + nested type.

Sample:
classes:

public class MyViewModel<T>
{
    public class Nested
    {
        Nested() { }
    }
}

in code-behind:
BindingContext = new MyViewModel<MyModel>.Nested()
In Xaml, I want to bind
x:DataType="{x:Type viewmodels:MyViewModel(models:MyModel)+Nested"
See also #16841 #20625 #20616

[bmacombe]

Hey @BaY1251 I too had trouble finding the correct syntax for referencing a nested type. Here is an example.

x:DataType="testSubmission:TestSubmissionsViewModel+SubmissionDisplay"