added type hints for Blenderbot and BlenderbotSmall (TF & PyTorch)
Author: IvanLauLinTiong
Pull request: yes

# What does this PR do?

Added type hints for Blenderbot and BlenderbotSmall Tensorflow & PyTorch as described in https://github.com/huggingface/transformers/issues/16059

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@Rocketknight1 @gante 

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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:
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_16273). All of your documentation changes will be reflected on that endpoint.

Hi @IvanLauLinTiong, we actually just merged a BART PR that covers the same changes! It's probably easiest if you take a look at the most recent changes and see if a separate BlenderBot PR is needed - if so, you can make a new PR on a new branch that just changes BlenderBot and copy your changes over.

It's unfortunate, though - this looks like a really solid PR, but I just got two PRs covering BART at the same time!

Hi @Rocketknight1 , haha ok noted. I will try take a look at the recent changes and see what I can do here at BlenderBot model.