Improvements around DBNull.Value for DataRowExtensions

[roji]

Closes #9077

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Issue Details

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Closes #9077

Author:	roji
Assignees:	roji
Labels:	area-System.Data
Milestone:	-

[learn-build-service-prod]

Learn Build status updates of commit f6e6e9b:

✅ Validation status: passed

File	Status	Preview URL	Details
xml/System.Data/DataRowExtensions.xml	✅Succeeded	View

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[JRahnama]

LGTM, just a minor question, : according to the comment from VS team in issue #2013 at SqlClient cref should be used instead of xref. That is going to be a lot of work to updated the entire documentation, but we can stop adding more to it I think. Again this is going to be huge. For example, instead of CDATA, each paragraph should be wrapped in <para>[content]</para> tags and some other modifications. I am just wondering if we should start following that path to prevent more changes to convert in future?

[roji]

@JRahnama I'm not an expert on the doc system - someone more proficient there should probably answer. But if indeed a fundamental change like that needs to be done, I think it would be better to do that in a separate dedicated PR that does everything.. This PR really is unrelated to that, and changing things here would lead to an inconsistent state where we don't do the same thing everywhere..