[Feature] Add functionality to use AAD B2C authentication

[tnsturm]

AAD-B2C-specifics

Please add some overloads to MSALProvider constructor and GetTokenAsync:

AAD B2C needs the bold marked specifics:

application = PublicClientApplicationBuilder.Create(ClientID)
.WithB2CAuthority(Authority)
.Build();

and

await application.GetAccountsAsync( B2CPolicySignUpSignIn );

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[michael-hawker]

@tnsturm I believe you're talking about this API here?

I believe this requires us to update our dependency to enable, though I know there's a change in how MSAL is packaged, so I'm not familiar with which side of that gap we're on.

Not sure if @shweaver-MSFT remembers.

[shweaver-MSFT]

I suggest either:

1. Create the PublicClientApplication object externally and pass it into the constructor.
   

   Graph-Controls/CommunityToolkit.Authentication.Msal/MsalProvider.cs

   Line 63 in 15513b1

   public MsalProvider(IPublicClientApplication client, string[] scopes = null, bool autoSignIn = true)

2. Extend MsalProvider and override the CreatePublicClientApplication function to add this functionality. Something like a "B2CMsalProvider". You can reference the original method to see how we do it and add in the line you need:
   

   Graph-Controls/CommunityToolkit.Authentication.Msal/MsalProvider.cs

   Line 187 in 15513b1

   protected IPublicClientApplication CreatePublicClientApplication(string clientId, string tenantId, string redirectUri, bool listWindowsWorkAndSchoolAccounts)

If you still think this would make a good addition to the toolkit and have the energy, I'd love someone to take a second look at the problem, think about the issue, propose a fix and put up a PR. Let us know if that sounds interesting to you and feel free to continue the conversation here in this issue :)