Fix LSP references for using alias

[dibarbet]

No bug link, just hit error here when I was investigating something else. It was attempting to create a decompiled location for the definition because it had no DocumentSpan

2025-06-04 13:00:56.667 [info] [Error - 1:00:56 PM] [textDocument/references] [LSP] System.InvalidOperationException: Unexpected value 'MyType' of type 'Microsoft.CodeAnalysis.CSharp.Symbols.PublicModel.AliasSymbol'
   at Microsoft.CodeAnalysis.MetadataAsSource.MetadataAsSourceHelpers.GetTopLevelContainingNamedType(ISymbol symbol) in /_/src/Features/Core/Portable/MetadataAsSource/MetadataAsSourceHelpers.cs:line 51
   at Microsoft.CodeAnalysis.MetadataAsSource.DecompilationMetadataAsSourceFileProvider.GetGeneratedFileAsync(MetadataAsSourceWorkspace metadataWorkspace, Workspace sourceWorkspace, Project sourceProject, ISymbol symbol, Boolean signaturesOnly, MetadataAsSourceOptions options, String tempPath, TelemetryMessage telemetryMessage, CancellationToken cancellationToken) in /_/src/Features/Core/Portable/MetadataAsSource/DecompilationMetadataAsSourceFileProvider.cs:line 78
   at Microsoft.CodeAnalysis.MetadataAsSource.MetadataAsSourceFileService.GetGeneratedFileAsync(Workspace sourceWorkspace, Project sourceProject, ISymbol symbol, Boolean signaturesOnly, MetadataAsSourceOptions options, CancellationToken cancellationToken) in /_/src/Features/Core/Portable/MetadataAsSource/MetadataAsSourceFileService.cs:line 108
   at Microsoft.CodeAnalysis.LanguageServer.Handler.FindUsagesLSPContext.ComputeLocationAsync(Nullable`1 documentSpan, CancellationToken cancellationToken) in /_/src/LanguageServer/Protocol/Handler/References/FindUsagesLSPContext.cs:line 265