Doc styler examples (#14953)

* Fix bad examples

* Add black formatting to style_doc

* Use first nonempty line

* Put it at the right place

* Don't add spaces to empty lines

* Better templates

* Deal with triple quotes in docstrings

* Result of style_doc

* Enable mdx treatment and fix code examples in MDXs

* Result of doc styler on doc source files

* Last fixes

* Break copy from

docs/source/main_classes/output.mdx

@@ -22,8 +22,8 @@ Let's see of this looks on an example:
 from transformers import BertTokenizer, BertForSequenceClassification
 import torch
 
-tokenizer = BertTokenizer.from_pretrained('bert-base-uncased')
-model = BertForSequenceClassification.from_pretrained('bert-base-uncased')
+tokenizer = BertTokenizer.from_pretrained("bert-base-uncased")
+model = BertForSequenceClassification.from_pretrained("bert-base-uncased")
 
 inputs = tokenizer("Hello, my dog is cute", return_tensors="pt")
 labels = torch.tensor([1]).unsqueeze(0)  # Batch size 1