[generator] Support for generic classes in our block trampolines

[dalexsoto]

Binding UIKit brought some generic classes into the mix of our blocks support, see https://github.com/xamarin/xamarin-macios/pull/8992/files#diff-1ca9e8e46629c0f8806cee2c8be4aad3R22727-R22764.

Here is a proposed test case but we can adjust as needed.

    delegate T HelloGenericDelegate<T> () where T : NSObject;
    delegate T HelloGenericDelegate2<T> (T t1) where T : NSObject;
    delegate T1 HelloGenericDelegate3<T1, T2> (T1 t1, T2 t2) where T1 : NSObject where T2 : NSObject;
    delegate T1 HelloGenericDelegate4<T1, T2> (T1 t1, T2 t2, [BlockCallback] HelloGenericDelegate2<T1> otherBlock) where T1 : NSObject where T2 : NSObject;

    [BaseType(typeof(NSObject))]
    interface OneGenericType<T1>
        where T1 : NSObject
    {

    }

    [BaseType(typeof(NSObject))]
    interface Example<T1>
        where T1 : NSObject
    {

        [NullAllowed, Export("one", ArgumentSemantic.Copy)]
        Func<T1, bool> One { get; set; }

        [NullAllowed, Export("two", ArgumentSemantic.Copy)]
        Action<T1> Two { get; set; }

        [NullAllowed, Export("three", ArgumentSemantic.Copy)]
        Func<T1, OneGenericType<T1>, OneGenericType<T1>> Three { get; set; }

        [NullAllowed, Export("four", ArgumentSemantic.Copy)]
        HelloGenericDelegate<T1> Four { get; set; }

        [NullAllowed, Export("five", ArgumentSemantic.Copy)]
        HelloGenericDelegate2<T1> Five { get; set; }
    }

    interface TwoGenericsType<T1, T2>
        where T1 : NSObject
        where T2 : NSObject
    {
        
    }

    [BaseType(typeof(NSObject))]
    interface ExampleTwo<T1, T2>
        where T1 : NSObject
        where T2 : NSObject
    {

        [NullAllowed, Export("one", ArgumentSemantic.Copy)]
        Func<T1, bool, T2> One { get; set; }

        [NullAllowed, Export("two", ArgumentSemantic.Copy)]
        Action<T1, T2> Two { get; set; }

        [NullAllowed, Export("three", ArgumentSemantic.Copy)]
        Func<T1, T2, TwoGenericsType<T1, T2>, TwoGenericsType<T1, T2>> Three { get; set; }

        [NullAllowed, Export("four", ArgumentSemantic.Copy)]
        HelloGenericDelegate3<T1, T2> Four { get; set; }

        [NullAllowed, Export("five", ArgumentSemantic.Copy)]
        HelloGenericDelegate4<T1, T2> Five { get; set; }
    }