Implement fast tokenizer for Big Bird models
This issue is similar to #10498 


## Your contribution
I can help with the implementation. Can someone provide me the high-level steps ?
@stefan-it 

The way I would approach is to start from a copy-paste of a very similar fast tokenizer (it's based on SentencePiece, so ALBERT is an example of these), and adapt to Big Bird.

Feel free to open a PR in early stages and let us know if you run in any issues!<|||||>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.<|||||>> 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.

It is in progress in this [PR](https://github.com/huggingface/transformers/pull/11075)