Rollup merge of #102447 - notriddle:notriddle/method-toggle, r=jsha

rustdoc: add method spacing to trait methods

More cleanup for 8846c0853d, this time in trait layouts when things are collapsed.

This PR makes two changes to the appearance of trait pages:

* It adds the `method-toggle` class to method toggles on traits, making the DOM more consistent with type pages (which already have this class).

  ## Before

  ![image](https://user-images.githubusercontent.com/1593513/192914353-ed17e1eb-df1d-480b-9998-3b5e8283b0ee.png)

  ## After

  ![image](https://user-images.githubusercontent.com/1593513/192914570-bdd0f2e1-5254-4e2e-9576-a797b82b3b3b.png)

* It adds a bottom margin to docblocks nested directly in the implementors list, giving it a similar appearance to if it was nested within a toggle.

  ## Before

  ![image](https://user-images.githubusercontent.com/1593513/192914503-1c3f39d5-690f-44ec-8f11-385302477d04.png)

  ## After

  ![image](https://user-images.githubusercontent.com/1593513/192914702-cbce4b3b-5cc6-49dc-b7f8-73be9e76791c.png)

src/librustdoc/html/render/print_item.rs

@@ -716,7 +716,7 @@ fn item_trait(w: &mut Buffer, cx: &mut Context<'_>, it: &clean::Item, t: &clean:
         document(&mut content, cx, m, Some(t), HeadingOffset::H5);
         let toggled = !content.is_empty();
         if toggled {
-            write!(w, "<details class=\"rustdoc-toggle\" open><summary>");
+            write!(w, "<details class=\"rustdoc-toggle method-toggle\" open><summary>");
         }
         write!(w, "<div id=\"{}\" class=\"method has-srclink\">", id);
         render_rightside(w, cx, m, t, RenderMode::Normal);