added type hints for BART model
# What does this PR do?

I have added type hints for BART model (both in PyTorch and Tensorflow) as described in #16059 
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@Rocketknight1 

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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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@Rocketknight1 here is the PR which i've created since i am on Windows so i didnt run ``make fixup`` command<|||||>Hi @robotjellyzone, thanks for the PR! I see a lot of tests failing but I think that's our fault, not yours. Let me try running `make fixup` and then rerun them, and hopefully it all passes<|||||>_The documentation is not available anymore as the PR was closed or merged._<|||||>@robotjellyzone Tests pass now! Will merge and then update the other PRs depending on these copied models.