Fix LayoutLMv2 tokenization docstrings

[qqaatw]

What does this PR do?

The tokenizers of LayoutLMv2 don't accept is_split_into_words keyword for __call__. Thus, I created a dedicated kwargs docstring to replace the one in src/transformers/tokenization_utils_base.py being used.

Fixes # (issue)

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@NielsRogge @LysandreJik

[HuggingFaceDocBuilderDev]

The documentation is not available anymore as the PR was closed or merged.

[qqaatw]

Will open a follow-up PR for LayoutXLM after accepted and merged.

[SaulLu]

Thanks for fixing! 😄

[github-actions]

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.

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[LysandreJik]

@NielsRogge can you give this a look when you have a minute?

[NielsRogge]

Thanks for fixing :) can you rebase with the main branch, such that we can merge your PR?

[qqaatw]

Done.

[NielsRogge]

Seems like you changed some files which shouldn't be changed, like index.mdx. Could you fix those, please?

[NielsRogge]

Thanks, merging!