AutoImageProcessor (#20111)

* AutoImageProcessor skeleton

* Update references

* Add mapping in init

* Add model image processors to __init__ for importing

* Add AutoImageProcessor tests

* Fix up

* Image Processor documentation

* Remove pdb

* Update docs/source/en/model_doc/mobilevit.mdx

* Update docs

* Don't add whitespace on json files

* Remove fixtures

* Move checking model config down

* Fix up

* Add check for image processor

* Remove FeatureExtractorMixin in docstrings

* Rename model_tmpfile to config_tmpfile

* Don't make None if not in image processor map

docs/source/en/model_doc/layoutlmv2.mdx

@@ -45,7 +45,7 @@ RVL-CDIP (0.9443 -> 0.9564), and DocVQA (0.7295 -> 0.8672). The pre-trained Layo
 this https URL.*
 
 LayoutLMv2 depends on `detectron2`, `torchvision` and `tesseract`. Run the
-following to install them: 
+following to install them:
 ```
 python -m pip install 'git+https://github.com/facebookresearch/detectron2.git'
 python -m pip install torchvision tesseract
@@ -275,6 +275,11 @@ print(encoding.keys())
 [[autodoc]] LayoutLMv2FeatureExtractor
     - __call__
 
+## LayoutLMv2ImageProcessor
+
+[[autodoc]] LayoutLMv2ImageProcessor
+    - preprocess
+
 ## LayoutLMv2Tokenizer
 
 [[autodoc]] LayoutLMv2Tokenizer