Update pipeline word heuristic to work with whitespace in token offsets
# What does this PR do?

This change checks for whitespace in the input string at either the
character preceding the token or in the first character of the token.
This works with tokenizers that return offsets excluding whitespace
between words or with offsets including whitespace.

Fixes #18111

## Before submitting
- [ ] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
- [x] Did you read the [contributor guideline](https://github.com/huggingface/transformers/blob/main/CONTRIBUTING.md#start-contributing-pull-requests),
      Pull Request section?
- [x] Was this discussed/approved via a Github issue or the [forum](https://discuss.huggingface.co/)? Please add a link
      to it if that's the case.
- [ ] Did you make sure to update the documentation with your changes? Here are the
      [documentation guidelines](https://github.com/huggingface/transformers/tree/main/docs), and
      [here are tips on formatting docstrings](https://github.com/huggingface/transformers/tree/main/docs#writing-source-documentation).
- [x] Did you write any new necessary tests?


## Who can review?

Anyone in the community is free to review the PR once the tests have passed. Feel free to tag
members/contributors who may be interested in your PR.

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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
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_The documentation is not available anymore as the PR was closed or merged._<|||||>The tests failures seem to have nothing to do with this PR.

@LysandreJik @ydshieh  maybe ?<|||||>@LysandreJik @ydshieh @Narsil I think the test failures are because I set up CircleCI to track my fork, just to see if the tests would pass there. I didn't expect it to show here on the upstream project PR, but I think that might be what we're seeing. I've disabled that for any future commits.

I'm guessing failures on a hosted, free CircleCI project are expected, right? Sorry for the CI spam.<|||||>
> I'm guessing failures on a hosted, free CircleCI project are expected, right? Sorry for the CI spam.

Probably yes: I saw you have `Docker / [Docker Medium]` while `transformers` uses `Docker / [Docker X-Large]`.

Now we have to make the tests run under Hugging Face's CircleCI plan 😄 
<|||||>Ugh, so that stopped the HF circleci from firing? I can add a "maybe this time" commit, as is traditional with CI workflows...<|||||>Ok all that's left before merging is a final approval from a core maintainer.

@sgugger maybe ?