Injection duplicates do not emit any errors

In relation to the report: https://github.com/dotnet/aspnetcore/issues/63445.

To reproduce you can use the current net10 identity template or just duplicate any `@inject` property name in Razor file of your choice. The IDE will underline the duplicate but the compilation won't produce any errors. We don't have this behavior documented. Do we want to fix it by producing an error, instead of ignoring the duplicates in https://github.com/dotnet/razor/blob/c150d2096536ce3e0fb5b1007d4e39663f22bcaa/src/Compiler/Microsoft.CodeAnalysis.Razor.Compiler/src/Mvc/InjectDirective.cs#L81?

Reproduce the issue with the current net10 identity template or a Razor file containing duplicate @inject property names, then inspect InjectDirective.cs at the linked line where duplicates are ignored. Check the related ASP.NET Core report for context; done means compilation reports an error for duplicate injection properties instead of silently ignoring them.

Written by the indexing model from the issue text.