Add AutoSuspendHelper to ReactiveUI.XamForms

[worldbeater]

What kind of change does this PR introduce?

This PR adds a new AutoSuspendHelper utility class to the ReactiveUI.XamForms package. In the proposed implementation we rely on Xamarin.Forms app lifecycle events https://docs.microsoft.com/en-us/xamarin/xamarin-forms/app-fundamentals/app-lifecycle

What is the current behavior?

Currently, AutoSuspendHelper implementations exist for iOS and Android as separate classes. An implementation targeting Xamarin.Forms could help to reduce the amount of platform-specific code as stated in #1429 and also this way we can support other platforms supported by XF.

What is the new behavior?

Now, there is an implementation of AutoSuspendHelper that works with Xamarin.Forms. Expected usage:

public partial class App : Application
{
    private readonly AutoSuspendHelper _autoSuspendHelper;

    public App()
    {
        _autoSuspendHelper = new AutoSuspendHelper();
        RxApp.SuspensionHost.CreateNewAppState = () => new MainState();
        RxApp.SuspensionHost.SetupDefaultSuspendResume(new CustomSuspensionDriver());
        _autoSuspendHelper.OnCreate();
    
        InitializeComponent();
        var state = RxApp.SuspensionHost.GetAppState<AppState>();
        MainPage = new MainView(new MainViewModel(state));
    }
    
    protected override void OnStart() => _autoSuspendHelper.OnStart();
    
    protected override void OnResume() => _autoSuspendHelper.OnResume();
    
    protected override void OnSleep() => _autoSuspendHelper.OnSleep();
}

What might this PR break?

Nothing.

Please check if the PR fulfills these requirements

• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

[codecov]

Codecov Report

Merging #2523 into main will not change coverage.
The diff coverage is n/a.

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  Lines        4572     4572           
  Branches      802      802           
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  Hits         2415     2415           
  Misses       1913     1913           
  Partials      244      244           

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[glennawatson]

Last time I checked this was held up by #1133. Is it fixed now?

[worldbeater]

@glennawatson curious how data persistence may relate to XF view activation? Always thought ReactiveUI data persistence is a separate feature which only depends on lifecycle events of an application, according to AutoSuspendHelper implementation used in ReactiveUI.AndroidSupport, and also according to AutoSuspendHelper implementation used in iOS. Tested the implementation in a separate XF project and so far it worked (but probably I was a bit naive and didn't test some edge cases).

[github-actions]

This pull request has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.