Correct & Improve Doctests for LayoutLMv2 (#17168)
* add inference example to LayoutLMv2ForQuestionAnswering, passing doctest
* add loss example to LayoutLMv2ForQuestionAnswering, passing doctest
* Add correct doctest for LayoutLMv2ForTokenClassification, passing doctest
* add correct doctest for LayoutLMv2ForSequenceClassification, passing test
* add correct doctest for LayoutLMv2Model, passing test
* make fixup
* fix to address review comments
* make style
* fix doctest line break issue, add to documentaiton_tests.txt, address review comments
* move comment about layoutlmv2 dependencies to the doc page
* format doc page as suggested
Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>
* delete extraneous backtick
Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>
