[docs] Fix BatchEncoding documentation inconsistencies (#47647)
* [docs] Fix BatchEncoding docstring inconsistencies
* Update src/transformers/tokenization_utils_base.py
Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>
---------
Co-authored-by: Steven Liu <59462357+stevhliu@users.noreply.github.com>