Update documentation/samples: Authority/Instance/TenantId precedence for AAD/B2C, warning logs

[jmprieur]

Background

As described in @AzureAD/microsoft-identity-web#3609 and sub-issues, correct Authority config—especially with conflicting values—should be made clear in documentation/samples. This includes both AAD and deprecated-but-supported B2C cases, as well as warning log diagnostics.

Doc updates and samples to cover

• Guidance on Authority-only vs Instance/TenantId for AAD
• Specific warning log output and fallback precedence
• Authority config for B2C (with policy, /tfp/) and how precedence works
• Migration guidance for customers moving off B2C path in future
• API XML comments for Authority, Instance, TenantId
• Troubleshooting section for warning logs
• Sample code blocks for valid/invalid configs

Sample content

option.Authority = "https://login.microsoftonline.com/tenant/v2.0";
// OR
option.Instance = "https://login.microsoftonline.com/";
option.TenantId = "tenant";

// B2C example
option.Authority = "https://contoso.b2clogin.com/tfp/contoso.onmicrosoft.com/B2C_1_signup_signin/v2.0";
option.DefaultUserFlow = "B2C_1_signup_signin";

Acceptance Criteria

• API docs clarify fallback logic and warning
• Wiki/MD guide covers both AAD and B2C
• Samples for correct configs and guidance on detecting warning logs
• Migration note for B2C

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Bridge: Propose concrete doc block diffs and sample code when Jean-Marc replies "Go ahead".