由于到目前为止还没有提出任何改进建议，以下是我最初的工作方法-只是为了完整起见：

private static ConcurrentBag<INamedTypeSymbol> GetImplementingSymbols(Project project)
{
    var compilation = project.GetCompilationAsync().Result;
    var typeToLookFor = compilation.GetTypeByMetadataName(typeof(IAnyInterface).FullName);

    var assemblySymbols =
        project.MetadataReferences
            .Select(compilation.GetAssemblyOrModuleSymbol)
            .OfType<IAssemblySymbol>()
            .ToList();

    assemblySymbols.Add(compilation.Assembly);

    var foundSymbols = new ConcurrentBag<INamedTypeSymbol>();

    Parallel.ForEach(assemblySymbols, symbol =>
    {
        var getAllSymbolsVisitor = new GetAllSymbolsVisitor(typeToLookFor, foundSymbols);
        getAllSymbolsVisitor.Visit(symbol.GlobalNamespace);
    });

    return foundSymbols;
}

private class GetAllSymbolsVisitor : SymbolVisitor
{
    private readonly ConcurrentBag<INamedTypeSymbol> _symbols;
    private INamedTypeSymbol _type;

    public GetAllSymbolsVisitor(INamedTypeSymbol type, ConcurrentBag<INamedTypeSymbol> symbols)
    {
        _symbols = symbols;
        _type = type;
    }

    public override void VisitNamespace(INamespaceSymbol symbol)
    {
        foreach (var namespaceOrTypeSymbol in symbol.GetMembers())
        {
            namespaceOrTypeSymbol.Accept(this);
        }
    }

    public override void VisitNamedType(INamedTypeSymbol symbol)
    {
        if (symbol.Interfaces.Any(interfaceType => SymbolEqualityComparer.Default.Equals(_type, interfaceType)))
        {
            _symbols.Add(symbol);
        }
    }
}