Blazor WASM AAD B2C user flows

[guardrex]

Fixes #17522

Based on Javier's remark here 👉 #17522 (comment)

If we get feedback that devs are having trouble implementing something (and if the framework doesn't provide a thing for this), then we can add an example. I hacked around with it, and just getting the challenge and callback to work wasn't too bad 👉 #17522 (comment)

cc: @Alienroid ... would u like to take a look at this and add your feedback? I think we just need to say for now that it isn't supported OOB and here's some guidance on making a challenge.

[guardrex]

@mkArtakMSFT I'm going to go ahead and merge this. It's low-hanging fruit at this point ...

The Microsoft Authentication Library (Microsoft.Authentication.WebAssembly.Msal) doesn't support [AAD B2C user flows](/azure/active-directory-b2c/user-flow-overview) by default. Create custom user flows in developer code.

For more information on how to build a challenge for a custom user flow, see [User flows in Azure Active Directory B2C](/azure/active-directory-b2c/user-flow-overview).

We can add an example of this later if readers are having trouble. For example, my hacks on the issue follow Javier's approach of reading the Azure AD result from the query string using a QueryStringHelper class. Devs might not find it easily grokable that they need to set response_type to query and use a query string parser like that. I'll keep an 👂 open for feedback.