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/model_doc/layoutlm.mdx

@@ -53,12 +53,12 @@ Tips:
 
 ```python
 def normalize_bbox(bbox, width, height):
-     return [
-         int(1000 * (bbox[0] / width)),
-         int(1000 * (bbox[1] / height)),
-         int(1000 * (bbox[2] / width)),
-         int(1000 * (bbox[3] / height)),
-     ]
+    return [
+        int(1000 * (bbox[0] / width)),
+        int(1000 * (bbox[1] / height)),
+        int(1000 * (bbox[2] / width)),
+        int(1000 * (bbox[3] / height)),
+    ]
 ```
 
 Here, `width` and `height` correspond to the width and height of the original document in which the token