`SelectionModel` can have a selection set before its `Source` is initialized. In this case, be sure to trim invalid selections from the model before continuing.
Fixes#3919
Make sure the item we're selecting is within the requested range. Also refactored the unit tests to do a simple test on `SelectedIndices` instead of using `IsSelectedWithPartial` because both can't really be tested together using the old testing method.
Make `SelectionModelChildrenRequestedEventArgs.Children` an observable, so that the we can react to the children collection object changing, as well as the children inside the collection changing.
Upstream issue: https://github.com/microsoft/microsoft-ui-xaml/issues/2404
`SelectionModel` as ported from WinUI has no information about what changed in a `SelectionChanged` event. This adds that information along with unit tests.
`SelectionModel` as ported from WinUI has no information about what changed in a `SelectionChanged` event. This adds that information along with unit tests.
Steven Kirk
Deadpikle