following #27539 this PR adds updates to transformers documentation to reflect possibility of utilizing 4D masks.

Plan:

• add updates for Llama model docstring(s)
• identify other models that can use 4D masks in present form (which requires ability to accept custom position_ids argument) and updating their docstrings. Classes that need updates:
  • Falcon Model
  • [TODO identify more]
• update code comments that may need corrections, like cases where the mask may be either 2D or 4D now. one example is based on this comment by @shentianxiao

Update 20.12.2023:
to find out which models require docstring changes, I scanned all model classes in transformers insing inspect.

• excluded tf and jax classes
• excluded models without position_ids argument in .forward() - can't use 4D mask effectively
• excluded models that do not use _prepare_4d_attention_mask method - need different code change to use 4D mask
• excluded multi-modal models (clip, clvp, vit, bark, git)

what is left is LlamaModel, FalconModel and XGLMModel.

cc @ArthurZucker