WN9.7: Move non-blazor embedded snippets to project

[Rick-Anderson]

Description

Our policy is to NOT use embedded snippets. For .NET 10 previews, we should aim to have Compilable code :::code language="csharp" source="~/fundamentals/Program.cs" id="snippet_1" highlight="1":::

Every snipped I migrated to a project had at least 1 compiler error I fixes.
Record how many snippets you had to change here.

Page URL

https://learn.microsoft.com/en-us/aspnet/core/release-notes/aspnetcore-9.0?view=aspnetcore-8.0

Content source URL

https://github.com/dotnet/AspNetCore.Docs/blob/main/aspnetcore/release-notes/aspnetcore-9.0.md

Document ID

4e75ad25-2c3f-b28e-6a91-ac79a9c683b6

Article author

@Rick-Anderson

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Associated WorkItem - 302691

[wadepickett]

What's new PR entries where I also moved the code to projects and linked back in. For each one the code sample was created inline by the dev team and I went back and created an ASP.NET project for it with working code, tested and linked the code back in.

PR #33318
Moved the original inline code from dev for What's New .NET 9 Prev 7 for the SignalR section to a project that was compiled and tested.

PR #33460
Moved the original inline code from dev for What's New .NET 9 RC1 for WebSockets Keep-Alive Timeout to a project.

PR #34183
Recreated both SignalR ActivitySource examples for both client and server into an app project and the linked back in.