rustdoc: CSS: show the <details> "triangle" in all cases

Currently we use `<details>` and `<summary>` for the unstable
info box, under class `.stab`. However, they can also be useful
to add detailed documentation like lengthy detailed examples
that would be too much to show by default, e.g.:

    /// <details><summary>Time-threads diagram</summary>
    ///
    /// ```text
    /// // Thread 1             |  // Thread 2
    /// let _rg = lock.read();  |
    ///                         |  // will block
    ///                         |  let _wg = lock.write();
    /// // may deadlock         |
    /// let _rg = lock.read();  |
    /// ```
    /// </details>

See rust-lang#82624 for an example
where we could use this functionality.

Signed-off-by: Miguel Ojeda <[email protected]>

Author: ojeda

src/librustdoc/html/static/rustdoc.css

@@ -148,6 +148,7 @@ p {
 }
 
 summary {
+	display: list-item;
 	outline: none;
 }
 
@@ -834,10 +835,6 @@ body.blur > :not(#help) {
 	display: inline;
 }
 
-.stab summary {
-	display: list-item;
-}
-
 .stab .emoji {
 	font-size: 1.5em;
 }