add MobileNetV2 model (#17845)

* add model files etc for MobileNetV2

* rename files for MobileNetV1

* initial implementation of MobileNetV1

* fix conversion script

* cleanup

* write docs

* tweaks

* fix conversion script

* extract hidden states

* fix test cases

* make fixup

* fixup it all

* rename V1 to V2

* fix checkpoints

* fixup

* implement first block + weight conversion

* add remaining layers

* add output stride and dilation

* fixup

* add tests

* add deeplabv3+ head

* a bit of fixup

* finish deeplab conversion

* add link to doc

* fix issue with JIT trace

in_height and in_width would be Tensor objects during JIT trace, which caused Core ML conversion to fail on the remainder op. By making them ints, the result of the padding calculation becomes a constant value.

* cleanup

* fix order of models

* fix rebase error

* remove main from doc link

* add image processor

* remove old feature extractor

* fix converter + other issues

* fixup

* fix unit test

* add to onnx tests (but these appear broken now)

* add post_process_semantic_segmentation

* use google org

* remove unused imports

* move args

* replace weird assert

utils/documentation_tests.txt

@@ -107,6 +107,7 @@ src/transformers/models/megatron_bert/configuration_megatron_bert.py
 src/transformers/models/mobilebert/configuration_mobilebert.py
 src/transformers/models/mobilebert/modeling_mobilebert.py
 src/transformers/models/mobilebert/modeling_tf_mobilebert.py
+src/transformers/models/mobilenet_v2/modeling_mobilenet_v2.py
 src/transformers/models/mobilevit/modeling_mobilevit.py
 src/transformers/models/mobilevit/modeling_tf_mobilevit.py
 src/transformers/models/nezha/configuration_nezha.py