fix(auth): deprecate Microsoft provider method not used for authentication

[russellwheatley]

Description

Flutter Auth documentation already uses correct sign-in method: https://firebase.google.com/docs/auth/flutter/federated-auth?#microsoft

Both Firebase android and iOS documentation use provider to sign-in with Microsoft.

Firebase documentation states you cannot use access token based credentials to sign in: https://firebase.google.com/docs/auth/ios/microsoft-oauth?_gl=1*1rjsp43*_up*MQ..*_ga*OTM3NzY0NDIuMTczOTUzMjc1Mw..*_ga_CW55HF8NVT*MTczOTUzMjc1My4xLjAuMTczOTUzMjc1My4wLjAuMA..#expandable-2

Related Issues

closes #16598

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