Add image classifier donut & update loss calculation for all swins (#37224)

* add classifier head to donut

* add to transformers __init__

* add to auto model

* fix typo

* add loss for image classification

* add checkpoint

* remove no needed import

* reoder import

* format

* consistency

* add test of classifier

* add doc

* try ignore

* update loss for all swin models

docs/source/en/model_doc/donut.md

@@ -226,3 +226,8 @@ print(answer)
 
 [[autodoc]] DonutSwinModel
     - forward
+
+## DonutSwinForImageClassification
+
+[[autodoc]] transformers.DonutSwinForImageClassification
+    - forward