Fixing object detection with layoutlm.
Author: Narsil
Pull request: yes

# What does this PR do?

Fixes the slow test by making sure we're loading the FeatureExtractor.

`LayoutLM` doesn't have a `FeatureExtractor` while `LayoutLMV2` does and this repo uses a combination of both.

Putting `LayoutLM` in the MULTI_MODAL config enables the pipeline to load `feature_extractor` regardless of `FEATURE_EXTRACTION_MAPPING`.

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Fixes # (issue)


## Before submitting
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Models:

- text models: @ArthurZucker and @younesbelkada
- vision models: @amyeroberts and @NielsRogge
- speech models: @sanchit-gandhi

Library:

- flax: @sanchit-gandhi
- generate: @gante
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- tokenizers: @ArthurZucker
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HF projects:

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Comments:
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