[SwiftBindings] Hande TypeMetadata for tuples

[stephen-hawley]

In TypeMetadata.cs in TryGetTypeMetadataUncached add code like this:

if (IsTuple(type)) {
    return TryGetTupleMetadata(type, out result);
}

// ...

static bool IsTuple(Type type)
{
}

static bool TryGetTupleMetadata(Type type, [NotNullWhen(true)] out TypeMetadata? result)
{
}