Add GLPN (#16199)

* First draft

* Fix logits calculation

* Improve tests

* Add copied from statements

* Fix base_model_prefix

* Improve implementation, upload new models

* Update design

* Fix integration test

* Add model to README and toctree

* Add document image

* Apply suggestions from code review

* Apply suggestions from code review

Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>

* Add decoder_hidden_size attribute

* Update design of decoder

* Add DepthEstimatorOutput class

* Rename in_index to head_in_index and add feature extractor tests

* Apply suggestions from code review

* Apply suggestions from code review

* Update pretrained model name and add to doc tests

* Remove test.py script

* Update copied from statements and clean up

Co-authored-by: Niels Rogge <nielsrogge@Nielss-MacBook-Pro.local>
Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>

utils/documentation_tests.txt

@@ -34,3 +34,16 @@ src/transformers/models/wav2vec2/modeling_wav2vec2.py
 src/transformers/models/wav2vec2/tokenization_wav2vec2.py
 src/transformers/models/wav2vec2_with_lm/processing_wav2vec2_with_lm.py
 src/transformers/models/wavlm/modeling_wavlm.py
+src/transformers/models/bart/modeling_bart.py
+src/transformers/models/mbart/modeling_mbart.py
+src/transformers/models/bigbird_pegasus/modeling_bigbird_pegasus.py
+src/transformers/models/marian/modeling_marian.py
+src/transformers/models/pegasus/modeling_pegasus.py
+src/transformers/models/blenderbot/modeling_blenderbot.py
+src/transformers/models/blenderbot_small/modeling_blenderbot_small.py
+src/transformers/models/plbart/modeling_plbart.py
+src/transformers/generation_utils.py
+docs/source/quicktour.mdx
+docs/source/task_summary.mdx
+src/transformers/models/resnet/modeling_resnet.py
+src/transformers/models/glpn/modeling_glpn.py