Feature Request: Generic ListView<T> with typed Value, SelectedItem

[YourRobotOverlord]

Summary

Add a generic ListView<T> that extends ListView and implements IValue<T>, so the selected item is exposed as the actual object of type T rather than as an integer index.

Also add an AspectGetter (Func<T,string>?) delegate to ListWrapper<T> and ListView<T> so developers can control how items are converted to display text without writing a custom IListDataSource.

Motivation

The existing ListView exposes selection as int? Value / int? SelectedItem (an index). When the underlying data is a typed collection, callers must keep the collection and the list in sync manually and cast back to get the selected object. A generic ListView<T> eliminates that friction:

`csharp
// Before
listView.SelectedItem = 2;
MyObject selected = myCollection[listView.SelectedItem!.Value];

// After
ListView listView = new ();
listView.SetSource(myCollection);
MyObject? selected = listView.Value;
`

Similarly, ListWrapper<T> currently calls ToString() unconditionally. For domain objects, ToString() is rarely suitable for display, forcing developers to implement a full custom IListDataSource just to change one string:

csharp // Before: full custom IListDataSource required // After listView.AspectGetter = obj => obj.Name;

Proposed API

ListView<T> : ListView, IValue<T>

Member	Type	Notes
Value	new T?	Primary — the selected object
SelectedItem	new T?	Convenience alias for Value
Index	int? (get/set)	Access the underlying int? index
AspectGetter	Func<T,string>?	Custom display-text converter
SetSource(ObservableCollection<T>?)	method	Typed source
ValueChanging	event EventHandler<ValueChangingEventArgs<T?>>	Typed, cancellable
ValueChanged	event EventHandler<ValueChangedEventArgs<T?>>	Typed

ListWrapper<T>.AspectGetter

csharp public Func<T, string>? AspectGetter { get; set; }

When set, used in Render() and GetMaxLengthItem() instead of ToString(). Fully backward-compatible (null by default).

Additional context

• SelectedItem mirrors the existing ListView doc: "a convenience property that is an alias for Value"
• Index is the way to get/set the int? index when using ListView<T>
• A UICatalog scenario demonstrating all features would be included
• No breaking changes to ListView or ListWrapper<T>