title: Support to load dataset with TSV files by passing only dataset name
comments: _The documentation is not available anymore as the PR was closed or merged._
body: This PR implements support to load a dataset (w/o script) containing TSV files by passing only the dataset name (no need to pass `sep='\t'`):
  ```python
  ds = load_dataset("dataset/name")
  ```
  
  The refactoring allows for future builder kwargs customizations based on file extension.
  
  Related to #4238.