HPCC-10142 queryLogicalFilename not supported on hthor

Refactor the code
    - Separate the superfile processing and use nested iterators
    - Separate single file processing
    - Remove leading '~' char from logical file name.

Tested with issue10142.ecl

Signed-off-by: Attila Vamos <attila.vamos@gmail.com>

if there's a dfIter, distFile can't be NULL, so I think it would be cleared if these 2 lines said:
````
if (dfIter)
{
    IDistributedFile * distFile = &dfIter->query();
````