[WIP] Flax XLM
Author: asvskartheek
Pull request: yes

# What does this PR do?
This PR will add XLM in Flax/Jax

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Fixes # (issue)


## Before submitting
- [ ] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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Models:

- albert, bert, xlm: @LysandreJik
- blenderbot, bart, marian, pegasus, encoderdecoder,  t5: @patrickvonplaten, @patil-suraj
- longformer, reformer, transfoxl, xlnet: @patrickvonplaten
- fsmt: @stas00
- funnel: @sgugger
- gpt2: @patrickvonplaten, @LysandreJik
- rag: @patrickvonplaten, @lhoestq
- tensorflow: @LysandreJik

Library:

- benchmarks: @patrickvonplaten
- deepspeed: @stas00
- ray/raytune: @richardliaw, @amogkam
- text generation: @patrickvonplaten
- tokenizers: @n1t0, @LysandreJik
- trainer: @sgugger
- pipelines: @LysandreJik

Documentation: @sgugger

HF projects:

- datasets: [different repo](https://github.com/huggingface/datasets)
- rust tokenizers: [different repo](https://github.com/huggingface/tokenizers)

Examples:

- maintained examples (not research project or legacy): @sgugger, @patil-suraj
- research_projects/bert-loses-patience: @JetRunner
- research_projects/distillation: @VictorSanh

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Comments:
Hey @asvskartheek 

Great to see that you started working on `FlaxXLM`! Feel free to ping me and @patrickvonplaten  if you have any questions! Happy to help :)

Hey @patil-suraj , thanks for offering to help. Is there a general guide or a series of standard steps that can follow while porting models to Flax on HuggingFace in HF's own style?

There is no guide as such yet. But you could see how other models are implemented in Flax, which should give a good idea about the conversion. Here's [FlaxBert](https://github.com/huggingface/transformers/blob/master/src/transformers/models/bert/modeling_flax_bert.py), [FlaxGPT2](https://github.com/huggingface/transformers/blob/master/src/transformers/models/bert/modeling_flax_bert.py)

To start you could just copy the PyTorch model and start replacing each module in Flax.

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.