[New Model] Add TimeSformer model (#18908)

* init timesformer

* apply fix-copies

* reformat style

* revert back some incoorect style updates

* init timesformer

* apply fix-copies

* reformat style

* revert back some incoorect style updates

* update timseformer doc

* add some functions and classes

* add new config params

* implement multiple classes

* update TimeSformerLayer

* update TimeSformerModel, TimeSformerPreTrainedModel, TimeSformerEncoder

* several fixes

* reformat

* temporary update

* fix some typos

* fix weight converter

* more fixes

* fix a typo

* fix typo

* remove redundant params

* fix for latest hf-hub

* merge fix

* fix some checks

* video classification works with einops

* add paper info to docs

* merge fix

* remove redundant line

* remove redundant docstring

* update config

* fix some typos

* fix converter

* update some test constants

* refactor einops functions

* reformat

* fix a comment

* remove redundat imports

* reformat

* fix a typo

* remove comment

* remove unused imports

* remove redundant doc line

* reformat

* add missing line

* fix docs

* fix timesformer auto feat ext

* add unittests

* reformat

* fix docs

* some fixes and updates

* fix readme

* fix modeling

* fix readme

* update index

* revert _toctree.yml changes

* update timseformer.mdx

* update drop_path_prob to drop_path_rate

* add dosctring for drop_path_rate

* update TimeSformerPatchEmbed naming

* remove to_2tuple

* explicit use of nn.functional

* reformat

* many updates from review comments

* fix a typo

* reformat

* remove assert, better variable name

* make variable names more explicit

* add some adapted from

* more explicit variable names

* remove redundant docstring

* fix initilaization

* move permute inside embedding

* update class names

* remove unused imports

* add test for video classification

* update PretrainedModel with PreTrainedModel

* remove double permute

* update based on sylvain's review

* aply auto fix

* update image_processing_auto for timesformer

* update hub urls

* reformat

* remove duplicate import

* update doc link

README_ko.md

@@ -341,7 +341,8 @@ Flax, PyTorch, TensorFlow 설치 페이지에서 이들을 conda로 설치하는
 1. **[TAPAS](https://huggingface.co/docs/transformers/model_doc/tapas)** (from Google AI) released with the paper [TAPAS: Weakly Supervised Table Parsing via Pre-training](https://arxiv.org/abs/2004.02349) by Jonathan Herzig, Paweł Krzysztof Nowak, Thomas Müller, Francesco Piccinno and Julian Martin Eisenschlos.
 1. **[TAPEX](https://huggingface.co/docs/transformers/model_doc/tapex)** (from Microsoft Research) released with the paper [TAPEX: Table Pre-training via Learning a Neural SQL Executor](https://arxiv.org/abs/2107.07653) by Qian Liu, Bei Chen, Jiaqi Guo, Morteza Ziyadi, Zeqi Lin, Weizhu Chen, Jian-Guang Lou.
 1. **[Time Series Transformer](https://huggingface.co/docs/transformers/model_doc/time_series_transformer)** (from HuggingFace).
-1. **[Trajectory Transformer](https://huggingface.co/docs/transformers/model_doc/trajectory_transformers)** (from the University of California at Berkeley) released with the paper [Offline Reinforcement Learning as One Big Sequence Modeling Problem](https://arxiv.org/abs/2106.02039) by Michael Janner, Qiyang Li, Sergey Levine
+1. **[TimeSformer](https://huggingface.co/docs/transformers/main/model_doc/timesformer)** (from Facebook) released with the paper [Is Space-Time Attention All You Need for Video Understanding?](https://arxiv.org/abs/2102.05095) by Gedas Bertasius, Heng Wang, Lorenzo Torresani.
+1. **[Trajectory Transformer](https://huggingface.co/docs/transformers/model_doc/trajectory_transformers)** (from the University of California at Berkeley) released with the paper [Offline Reinforcement Learning as One Big Sequence Modeling Problem](https://arxiv.org/abs/2106.02039) by Michael Janner, Qiyang Li, Sergey Levine 
 1. **[Transformer-XL](https://huggingface.co/docs/transformers/model_doc/transfo-xl)** (from Google/CMU) released with the paper [Transformer-XL: Attentive Language Models Beyond a Fixed-Length Context](https://arxiv.org/abs/1901.02860) by Zihang Dai*, Zhilin Yang*, Yiming Yang, Jaime Carbonell, Quoc V. Le, Ruslan Salakhutdinov.
 1. **[TrOCR](https://huggingface.co/docs/transformers/model_doc/trocr)** (from Microsoft), released together with the paper [TrOCR: Transformer-based Optical Character Recognition with Pre-trained Models](https://arxiv.org/abs/2109.10282) by Minghao Li, Tengchao Lv, Lei Cui, Yijuan Lu, Dinei Florencio, Cha Zhang, Zhoujun Li, Furu Wei.
 1. **[UL2](https://huggingface.co/docs/transformers/model_doc/ul2)** (from Google Research) released with the paper [Unifying Language Learning Paradigms](https://arxiv.org/abs/2205.05131v1) by Yi Tay, Mostafa Dehghani, Vinh Q. Tran, Xavier Garcia, Dara Bahri, Tal Schuster, Huaixiu Steven Zheng, Neil Houlsby, Donald Metzler