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/trainer.mdx

@@ -53,14 +53,16 @@ Here is an example of how to customize [`Trainer`] using a custom loss function
 from torch import nn
 from transformers import Trainer
 
+
 class MultilabelTrainer(Trainer):
     def compute_loss(self, model, inputs, return_outputs=False):
         labels = inputs.get("labels")
         outputs = model(**inputs)
-        logits = outputs.get('logits')
+        logits = outputs.get("logits")
         loss_fct = nn.BCEWithLogitsLoss()
-        loss = loss_fct(logits.view(-1, self.model.config.num_labels),
-                        labels.float().view(-1, self.model.config.num_labels))
+        loss = loss_fct(
+            logits.view(-1, self.model.config.num_labels), labels.float().view(-1, self.model.config.num_labels)
+        )
         return (loss, outputs) if return_outputs else loss
 ```