[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_repo.py

@@ -41,6 +41,8 @@ PRIVATE_MODELS = [
     "T5Stack",
     "SwitchTransformersStack",
     "TFDPRSpanPredictor",
+    "MaskFormerSwinModel",
+    "MaskFormerSwinPreTrainedModel",
 ]
 
 # Update this list for models that are not tested with a comment explaining the reason it should not be.
@@ -668,8 +670,11 @@ SHOULD_HAVE_THEIR_OWN_PAGE = [
     "PyTorchBenchmarkArguments",
     "TensorFlowBenchmark",
     "TensorFlowBenchmarkArguments",
+    "MaskFormerSwinBackbone",
     "ResNetBackbone",
     "AutoBackbone",
+    "MaskFormerSwinConfig",
+    "MaskFormerSwinModel",
 ]