Scanners should include file and offset information in errors

Currently we have to print the location of a parse error in BaseSequenceScanner::GetNextInternal():

state_->LogError(ErrorMsg(TErrorCode::SEQUENCE_SCANNER_PARSE_ERROR, 
    stream_->filename(), stream_->file_offset(),                    
    (stream_->eof() ? "(EOF)" : "")));                              

Instead, the scanners should include this information when constructing the error, which will allow us to simplify the error handling in the base class.