Rollup merge of rust-lang#129824 - GuillaumeGomez:code-example-button…

…s-mobile, r=notriddle

Fix code examples buttons not appearing on click on mobile

When browsing docs on mobile today, I realized that the buttons didn't appear when I tapped on the code example.

One issue: I have no idea how to add a regression test for this case...

r? ``@notriddle``

src/librustdoc/html/static/js/main.js

@@ -1878,9 +1878,15 @@ href="https://doc.rust-lang.org/${channel}/rustdoc/read-documentation/search.htm
         if (elem === null) {
             return;
         }
-        const buttons = elem.querySelector(".button-holder");
+        let buttons = elem.querySelector(".button-holder");
         if (buttons === null) {
-            return;
+            // On mobile, you can't hover an element so buttons need to be created on click
+            // if they're not already there.
+            addCopyButton(event);
+            buttons = elem.querySelector(".button-holder");
+            if (buttons === null) {
+                return;
+            }
         }
         buttons.classList.toggle("keep-visible");
     }