[DOCTEST] `configuration_layoutlm.py` , `configuration_layoutlmv2.py` ,` configuration_layoutlmv3.py`
Based on #19487 
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_19806). All of your documentation changes will be reflected on that endpoint.<|||||>cc @ydshieh 