Added GlobalProviderState to ProviderManager property for easy binding

Fixes #

PR Type

What kind of change does this PR introduce?

Feature

What is the current behavior?

SwitchPresenter from WCT doesn't work well with the GlobalProvider state as it exists today. It is not possible to simply use ProviderManager.Instance.GlobalProvider.State because the GlobalProvider.State is only available after the provider has been set, so the initial binding fails and updates are never processed.

What is the new behavior?

Use the new GlobalProviderState getter to retrieve the current state of the active GlobalProvider, or null if none.

This is helpful for binding in XAML, since GlobalProviderState is consistently available via the ProviderManager.Instance singleton.

<controls:SwitchPresenter Value="{x:Bind auth:ProviderManager.Instance.GlobalProviderState, Mode=OneWay}">

    <controls:Case Value="{x:Bind auth:ProviderState.SignedIn}">
        <TextBlock Text="Signed in!" />
    </controls:Case>

    <controls:Case Value="{x:Bind auth:ProviderState.SignedOut}">
        <TextBlock Text="Signed out" />
    </controls:Case>

    <controls:Case Value="{x:Bind auth:ProviderState.Loading}">
        <TextBlock Text="Loading..." />
    </controls:Case>

    <controls:Case IsDefault="True">
        <TextBlock Text="No provider is set" />
    </controls:Case>
</controls:SwitchPresenter>

PR Checklist

Please check if your PR fulfills the following requirements:

[x] Tested code with current supported SDKs
[ ] Sample in sample app has been added / updated (for bug fixes / features)
- [ ] Icon has been created (if new sample) following the Thumbnail Style Guide and templates
[ ] Tests for the changes have been added (for bug fixes / features) (if applicable)
[x] Header has been added to all new source files (run build/UpdateHeaders.bat)
[x] Contains NO breaking changes

CommunityToolkit / Graph-Controls