[Maui Blazor] Disable automatic package import when using the Razor SDK as it breaks Razor Class Libraries

https://github.com/dotnet/maui/issues/25999#issuecomment-3693107689

The workload changed to start bringing in the Webview.Maui package automatically which is designed for the final application and wreaks havoc when writing class libraries. Webview.Maui should be brought in explicitly by the app.

No file or test is named in the issue. Start by tracing the Razor SDK workload's automatic Webview.Maui package import, then verify that Razor Class Libraries no longer receive it implicitly while the final app can still bring it in explicitly. Use the linked discussion for the intended behavior and validation context.

Written by the indexing model from the issue text.