[Maskformer] Add MaskFormerSwin backbone (#20344)

* First draft

* Fix backwards compatibility

* More fixes

* More fixes

* Make backbone more general

* Improve backbone

* Improve test

* Fix config checkpoint

* Address comments

* Use model_type

* Address more comments

* Fix special model names

* Remove MaskFormerSwinModel and MaskFormerSwinPreTrainedModel from main init

* Fix typo

* Update backbone

* Apply suggestion

Co-authored-by: Niels Rogge <nielsrogge@Nielss-MacBook-Pro.local>

utils/check_copies.py

@@ -492,8 +492,9 @@ SPECIAL_MODEL_NAMES = {
     "Data2VecAudio": "Data2Vec",
     "Data2VecText": "Data2Vec",
     "Data2VecVision": "Data2Vec",
-    "DonutSwin": "Donut",
+    "DonutSwin": "Swin Transformer",
     "Marian": "MarianMT",
+    "MaskFormerSwin": "Swin Transformer",
     "OpenAI GPT-2": "GPT-2",
     "OpenAI GPT": "GPT",
     "Perceiver": "Perceiver IO",