Add OWL-ViT model for zero-shot object detection (#17938)

* add owlvit model skeleton

* add class and box predictor heads

* convert modified flax clip to pytorch

* fix box and class predictors

* add OwlViTImageTextEmbedder

* convert class and box head checkpoints

* convert image text embedder checkpoints

* add object detection head

* fix bugs

* update conversion script

* update conversion script

* fix q,v,k,out weight conversion conversion

* add owlvit object detection output

* fix bug in image embedder

* fix bugs in text embedder

* fix positional embeddings

* fix bug in inference mode vision pooling

* update docs, init tokenizer and processor files

* support batch processing

* add OwlViTProcessor

* remove merge conflicts

* readd owlvit imports

* fix bug in OwlViTProcessor imports

* fix bugs in processor

* update docs

* fix bugs in processor

* update owlvit docs

* add OwlViTFeatureExtractor

* style changes, add postprocess method to feature extractor

* add feature extractor and processor tests

* add object detection tests

* update conversion script

* update config paths

* update config paths

* fix configuration paths and bugs

* fix bugs in OwlViT tests

* add import checks to processor

* fix docs and minor issues

* fix docs and minor issues

* fix bugs and issues

* fix bugs and issues

* fix bugs and issues

* fix bugs and issues

* update docs and examples

* fix bugs and issues

* update conversion script, fix positional embeddings

* process 2D input ids, update tests

* fix style and quality issues

* update docs

* update docs and imports

* update OWL-ViT index.md

* fix bug in OwlViT feature ext tests

* fix code examples, return_dict by default

* return_dict by default

* minor fixes, add tests to processor

* small fixes

* add output_attentions arg to main model

* fix bugs

* remove output_hidden_states arg from main model

* update self.config variables

* add option to return last_hidden_states

* fix bug in config variables

* fix copied from statements

* fix small issues and bugs

* fix bugs

* fix bugs, support greyscale images

* run fixup

* update repo name

* merge OwlViTImageTextEmbedder with obj detection head

* fix merge conflict

* fix merge conflict

* make fixup

* fix bugs

* fix bugs

* add additional processor test

docs/source/en/index.mdx

@@ -130,6 +130,7 @@ The library currently contains JAX, PyTorch and TensorFlow implementations, pret
 1. **[NLLB](model_doc/nllb)** (from Meta) released with the paper [No Language Left Behind: Scaling Human-Centered Machine Translation](https://arxiv.org/abs/2207.04672) by the NLLB team.
 1. **[Nyströmformer](model_doc/nystromformer)** (from the University of Wisconsin - Madison) released with the paper [Nyströmformer: A Nyström-Based Algorithm for Approximating Self-Attention](https://arxiv.org/abs/2102.03902) by Yunyang Xiong, Zhanpeng Zeng, Rudrasis Chakraborty, Mingxing Tan, Glenn Fung, Yin Li, Vikas Singh.
 1. **[OPT](master/model_doc/opt)** (from Meta AI) released with the paper [OPT: Open Pre-trained Transformer Language Models](https://arxiv.org/abs/2205.01068) by Susan Zhang, Stephen Roller, Naman Goyal, Mikel Artetxe, Moya Chen, Shuohui Chen et al.
+1. **[OWL-ViT](model_doc/owlvit)** (from Google AI) released with the paper [Simple Open-Vocabulary Object Detection with Vision Transformers](https://arxiv.org/abs/2205.06230) by Matthias Minderer, Alexey Gritsenko, Austin Stone, Maxim Neumann, Dirk Weissenborn, Alexey Dosovitskiy, Aravindh Mahendran, Anurag Arnab, Mostafa Dehghani, Zhuoran Shen, Xiao Wang, Xiaohua Zhai, Thomas Kipf, and Neil Houlsby.
 1. **[Pegasus](model_doc/pegasus)** (from Google) released with the paper [PEGASUS: Pre-training with Extracted Gap-sentences for Abstractive Summarization](https://arxiv.org/abs/1912.08777) by Jingqing Zhang, Yao Zhao, Mohammad Saleh and Peter J. Liu.
 1. **[Perceiver IO](model_doc/perceiver)** (from Deepmind) released with the paper [Perceiver IO: A General Architecture for Structured Inputs & Outputs](https://arxiv.org/abs/2107.14795) by Andrew Jaegle, Sebastian Borgeaud, Jean-Baptiste Alayrac, Carl Doersch, Catalin Ionescu, David Ding, Skanda Koppula, Daniel Zoran, Andrew Brock, Evan Shelhamer, Olivier Hénaff, Matthew M. Botvinick, Andrew Zisserman, Oriol Vinyals, João Carreira.
 1. **[PhoBERT](model_doc/phobert)** (from VinAI Research) released with the paper [PhoBERT: Pre-trained language models for Vietnamese](https://www.aclweb.org/anthology/2020.findings-emnlp.92/) by Dat Quoc Nguyen and Anh Tuan Nguyen.
@@ -263,6 +264,7 @@ Flax), PyTorch, and/or TensorFlow.
 |         OpenAI GPT          |       ✅       |       ✅       |       ✅        |         ✅         |      ❌      |
 |        OpenAI GPT-2         |       ✅       |       ✅       |       ✅        |         ✅         |      ✅      |
 |             OPT             |       ❌       |       ❌       |       ✅        |         ✅         |      ✅      |
+|           OWL-ViT           |       ❌       |       ❌       |       ✅        |         ❌         |      ❌      |
 |           Pegasus           |       ✅       |       ✅       |       ✅        |         ✅         |      ✅      |
 |          Perceiver          |       ✅       |       ❌       |       ✅        |         ❌         |      ❌      |
 |           PLBart            |       ✅       |       ❌       |       ✅        |         ❌         |      ❌      |