[WIP] CLIP
# What does this PR do?

This PR adds OpenAI's CLIP model.
original repo: https://github.com/openai/CLIP
initial demo: https://colab.research.google.com/drive/1hwiCuKvw7hwSlE8yv7J1dh280PlYgPef?usp=sharing
Awesome effort. Is the current version already compatible with (now merged) #10594 ?<|||||>Thanks @dribnet 

I haven't added a feature extractor class for CLIP yet. We first need to finish the `ImageFeatureExtractor` (#01608)
Then the `ClipFeatureExtractor` can inherit from that. This PR will be ready to merge by the end of next week.<|||||>This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

Please note that issues that do not follow the [contributing guidelines](https://github.com/huggingface/transformers/blob/master/CONTRIBUTING.md) are likely to be ignored.<|||||>Unstale<|||||>continuing this in #11445 