Upgrade Facebook Graph API version to v21.0

[NSTom]

Upgrade Facebook Graph API version to v21.0

Currently, ASP.NET Core uses version v14.0 of the Facebook Graph API for authentication. This version of the API is no longer supported by Facebook, and should be upgraded to v21.0.

Description

Version v14.0 of the Graph API was supported until September 17, 2024. We should be able to safely upgrade to v21.0, the latest version, since there are no documented changes to the authorization, token or user information endpoints between these versions.

While this contributes towards #4684, it does not completely fix it, since the scope of that issue is broader than just Facebook.

[NSTom]

@microsoft-github-policy-service agree

[mkArtakMSFT]

Thanks for the PR, @NSTom.
@halter73 do we have an easy way to validate the change. While @NSTom mentioned that there are no documented breaking changes, the major version change (multiple versions, actually) is somewhat risky.
Maybe, as a safety measure, we can take this into main and ship in early .NET 10 previews to get customer validation for the scenario.

[dotnet-policy-service]

Looks like this PR hasn't been active for some time and the codebase could have been changed in the meantime.
To make sure no conflicting changes have occurred, please rerun validation before merging. You can do this by leaving an /azp run comment here (requires commit rights), or by simply closing and reopening.

[NSTom]

@dotnet-policy-service agree company="Funda Real Estate B.V."