Add X-Decoder Model 
### Model description

X-Decoder is a generalized decoding pipeline that can predict pixel-level segmentation and language tokens seamlessly. X-Decoder is the first work that provides a unified way to support all types of image segmentation and a variety of vision-language (VL) tasks. 

The model exhibits strong transferability to a wide range of downstream tasks in both zero-shot and fine-tuning settings, achieving state-of-the-art open-vocabulary segmentation and referring segmentation on 10 settings of 7 datasets and should be a valuable addition to transformers library

### Open source status

- [X] The model implementation is available
- [X] The model weights are available

### Provide useful links for the implementation

Paper: https://arxiv.org/pdf/2212.11270.pdf
Code: https://github.com/microsoft/X-Decoder
Weights: https://huggingface.co/spaces/xdecoder/Demo/blob/main/xdecoder_focalt_last.pt

Author: @eltociear 
Cc: @NielsRogge @alaradirik 
Hi @ChanBong, thanks for opening the issue!

You can expect to see an X-Decoder PR is the next two weeks :)<|||||>Hi @alaradirik, can we please collaborate in adding this model?<|||||>Hi @atharvakavitkar, the PR is almost done but won't include the _referring image editing_ task, which require integration with Stable Diffusion inpainting. Perhaps you could create a tutorial or demo for this task?<|||||>Hi @alaradirik, thank you for reaching out to me. I must admit that I have not yet added a model to HuggingFace. But I really want to learn how to do it. Would creating this tutorial be the right step? Or should I search for a simpler model to implement from scratch?