Feature Request : Increase the depth of information displayed in the sidebar

Hey,

Everytime I'm browsing the docs of transformers or datasets, I struggle to find the methods of the class I am using. This is even harder for classes with many methods like [Dataset](https://huggingface.co/docs/datasets/package_reference/main_classes#datasets.Dataset).

IMO, It would be more convenient to have the list of methods for the classes, a bit like what is done in Lightning or TorchMetrics where you can expand to see the list and navigate straight to the one you are looking for. Also it helps to have a grasp of all the methods available in a given class.

[Lightning example](https://lightning.ai/docs/pytorch/stable/common/lightning_module.html#methods) :