Light Freshness Edit: ASP.NET - migration & tutorials

[lootle1]

This PR contains freshness updates to the following articles:

• Migrate from ASP.NET Core in .NET 8 to ASP.NET Core in .NET 9
• Get started with NSwag and ASP.NET Core
• Part 7, add a new field to a Razor Page in ASP.NET Core
• Tutorial: Call an ASP.NET Core web API with JavaScript

Minor grammar/style updates. Link updates.
For request details, see 568764

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Internal previews

📄 File	🔗 Preview link
aspnetcore/migration/80-to-90.md	Migrate from ASP.NET Core in .NET 8 to ASP.NET Core in .NET 9