Reference articles from trim/AOT attribute docs

[sbomer]

Hopefully this helps with discoverability of the trimming docs. I am linking to https://learn.microsoft.com/dotnet/core/deploying/trimming/fixing-warnings rather than https://learn.microsoft.com/dotnet/core/deploying/trimming/prepare-libraries-for-trimming since I plan to remove parts of the latter.

@elinor-fung @agocke @vitek-karas PTAL.

[dotnet-issue-labeler]

I couldn't figure out the best area label to add to this PR. If you have write-permissions please help me learn by adding exactly one area label.

[learn-build-service-prod]

Learn Build status updates of commit 70a37bc:

✅ Validation status: passed

File	Status	Preview URL	Details
xml/System.Diagnostics.CodeAnalysis/DynamicallyAccessedMembersAttribute.xml	✅Succeeded	View
xml/System.Diagnostics.CodeAnalysis/RequiresDynamicCodeAttribute.xml	✅Succeeded	View
xml/System.Diagnostics.CodeAnalysis/RequiresUnreferencedCodeAttribute.xml	✅Succeeded	View
xml/System.Diagnostics.CodeAnalysis/UnconditionalSuppressMessageAttribute.xml	✅Succeeded	View

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