Add preview 2 features

[tdykstra]

contributes to #31770

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Internal previews

📄 File	🔗 Preview link
aspnetcore/release-notes/aspnetcore-9.0.md	What's new in ASP.NET Core 9.0

[guardrex]

NIT if you want to ... I'd recommend changing the broken sentence ("For example, the following code:" ... "Can now be simplified to the following code:") into two complete sentences. I suspect MT has a better shot if they're phrased as normal sentences.

[guardrex]

Side note for us all (@Rick-Anderson, @wadepickett) ... but u guys may already recall it ...

I was just reminded that under our new INCLUDE file scheme that updating an INCLUDE doesn't automatically update the Migration article. I'll probably flip the ms.date forward or backward or add/subtract a space at the end of a line to trigger the article to rebuild with an INCLUDE file change.

I made the Blazor Pre2 updates this morning (to the INCLUDE only). This PR will result in those changes being sucked into the article.

[danroth27]

[wadepickett]

Looks great with the update. Thanks Tom.