Test with the latest mdoc release

[BillWagner]

No description provided.

[joelmartinez]

This looks good to me, but I'll give someone else the opportunity to give the approval review ... there's only a handful of signature changes which are inline with recent changes (a few ref indexer changes, and one update to a vb signature to include FrameworkAlternate to match the rest of the MemberSignature entries). The rest are type forward metadata changes which was expected :)

[BillWagner]

Thanks @joelmartinez I'll look at the review site once the build is done and check the displayed versions of the changed APIs.

[joelmartinez]

after discussion with @BillWagner ... approving this :D

[carlossanlop]

@BillWagner - There were CI warnings in Span - the code snippets do not exist. They show up with a warning in the preview. Do we care about them for this update or can we address them later?:

https://review.docs.microsoft.com/en-us/dotnet/api/system.span-1?branch=pr-en-us-3998&view=netcore-3.1

File	Status	Preview URL	Details
api/System.Span-1.yml	Warning	View	[Warning] Cannot resolve ~/samples/snippets/csharp/api/system/span/program.cs relative to api/System.Span-1.yml.[Warning] Cannot resolve ~/samples/snippets/csharp/api/system/span/program.cs relative to api/System.Span-1.yml.[Warning] Cannot resolve ~/samples/snippets/csharp/api/system/span/program.cs relative to api/System.Span-1.yml.[Warning] Cannot resolve ~/samples/snippets/csharp/api/system/span/program.cs relative to api/System.Span-1.yml.[Warning] Cannot resolve ~/samples/snippets/csharp/api/system/span/slice/program.cs relative to api/System.Span-1.yml.[Warning] Cannot resolve ~/samples/snippets/csharp/api/system/span/slice2/program.cs relative to api/System.Span-1.yml.
api/System.Span-1.Enumerator.yml	Warning	View	[Warning] Cannot resolve ~/samples/snippets/csharp/api/system/span.enumerator/nosync/program.cs relative to api/System.Span-1.Enumerator.yml.[Warning] Cannot resolve ~/samples/snippets/csharp/api/system/span.enumerator/sync/program.cs relative to api/System.Span-1.Enumerator.yml.

[BillWagner]

@carlossanlop Those warnings are unrelated, but we are working on them now.

#3999 fixes most of these warnings. @Thraka is tracking down the remaining snippets.

Now that this PR has multiple conflicts, I'll close this and re-run the CI once we have the remaining snippets restored correctly.

The full plan for updating our snippets is in dotnet/docs#17297