Update Azure Active Directory documentation

[JunTaoLuo]

Issue description

In .NET 5.0 we have switched from using V1 AAD APIs to using Microsoft.Identity.Web as part of addressing https://github.com/dotnet/aspnetcore/issues/22726. Our templates have been updated to use Microsoft.Identity.Web and Microsoft.Identity.Web.UI instead of the obsolete Microsoft.AspNetCore.Authentication.AzureAD.UI and Microsoft.AspNetCore.Authentication.AzureADB2C.UI. We should update our documentation in this area to reflect the new APIs, see https://docs.microsoft.com/en-us/aspnet/core/security/authentication/azure-active-directory/

Software versions

Check the .NET target framework(s) being used, and include the version number(s).

• [x] .NET Core (.NET 5 covers both)
• [x] .NET Framework (.NET 5 covers both)
• [ ] .NET Standard

If using the .NET Core SDK, include dotnet --info output. If using .NET Framework without the .NET Core SDK, include info from Visual Studio's Help > About Microsoft Visual Studio dialog.

dotnet --info output or About VS info

```console ```

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Document Details

⚠ Do not edit this section. It is required for learn.microsoft.com ➟ GitHub issue linking.

• ID: 7bdae773-368b-a0c1-64d0-2a7b8c8fb134
• Version Independent ID: 2816eb27-7fc5-19e6-7f79-7e81a388647f
• Content: Microsoft identity platform and Azure Active Directory with ASP.NET Core
• Content Source: aspnetcore/security/authentication/azure-active-directory/index.md
• Product: aspnet-core
• Technology: aspnetcore-security
• GitHub Login: @Rick-Anderson
• Microsoft Alias: riande

[JunTaoLuo]

cc @Tratcher @jmprieur

[guardrex]

For Blazor security node topics, I'm tracking the work on [RC1] Microsoft Identity Platform 2.0 for Blazor (dotnet/AspNetCore.Docs #19503). I plan to work it shortly after RC1 lands.

[JunTaoLuo]

FYI it's not just blazor, this affects RazorPages, MVC, WebApi templates as well.

[guardrex]

Yes ... I'm just cross-linking the issue for visibility.