Add support to specify ItemsPanel for ItemsControl elements such as GridView

[pawisesa]

Summary

We're looking to use GridView as a radio for our app but we need to have the GridView and its GridViewItems to take the full width of the container and currently the GridView as implemented in react-native-xaml doesn't do that and there doesn't seem to be an option to configure it to take up the full width.

Looking into the XAML tree we see that the ItemsPresenter used by the react-native-xaml GridView currently is using ItemsWrapGrid and searching around it seems like a solution to make a GridView take up the full width in XAML is to use ItemsStackPanel instead for the GridView's ItemsPanel https://stackoverflow.com/a/35451090, however there's no option to set this for react-native-xaml currently.

There are multiple different possible Panel but for now only ItemsWrapGrid and ItemsStackPanel may be needed as options.

Motivation

This is needed to make GridView and other ItemsControl able to take up the full width of it's container. This would be useful for any user of GridView.

Basic Example

No response

Open Questions

No response

[chrisglein]

There's a lot of work here. It may be more straightforward for you to create a custom GridView that has the configuration you want. That'd also future proof you from any other gaps in react-native-xaml.

[pawisesa]

Will be making a custom GridView that uses ItemsStackPanel as the ItemsPanel.