Improve support for discard symbols

[Rekkonnect]

In the following code,

public class Program
{
    public static void Main(string[] args)
    {
        Method(out _);
    }
    
    private static void Method(out int value)
    {
        value = 3412;
    }
}

an IDiscardSymbol will be returned through the operation tree, or by selecting the _ alone and viewing the symbol info in the Details tab. This is not properly handled and can be prone to issues.