Throw Error When Adding Projects with the Same Name but Different Paths to Solution Folder

[hohosznta]

Description and customer impact

Fixes #47859

This ensures that Solution Folders do not allow adding a project that shares the same filename, regardless of its path. Before, adding the project to the solution using dotnet commands succeeded without errors, but building or opening it in Visual Studio produced errors or warnings. Now, it shows an error when adding duplicate filenames to solution folder via dotnet commands.
The existing test was originally intended to verify this behavior but had been skipped. I have now unskipped it.

[github-actions]

This PR is targeting main, which is now for .NET 11-facing work. If you intended to target .NET 10, either retarget this PR to release/10.0.1xx or make sure you backport the change to release/10.0.1xx after merging. See #50394 for more details.

[hohosznta]

I added a new CliString error message SolutionFolderAlreadyContainsProjectWithFilename since previously it didn't have a error ccase with solution folder, but it seems like it needs to be translated into various languages. Should I just use SolutionAlreadyContainsProject cliString?

[MiYanni]

Looks good to me.

Edit: You need to agree to the license/cla check for us to merge the code changes.

[MiYanni]

I added a new CliString error message SolutionFolderAlreadyContainsProjectWithFilename since previously it didn't have a error ccase with solution folder, but it seems like it needs to be translated into various languages. Should I just use SolutionAlreadyContainsProject cliString?

It is fine to add a new string. Our translation team will handle it just fine.

[hohosznta]

@dotnet-policy-service agree

[hohosznta]

Thanks, I have now agreed to the license. @MiYanni