rustdoc: small fixes to mobile navigation

- Make sure the mobile-topbar doesn't overflow its height if the user
  sets a bigger font.

- Make sure the sidebar can be scrolled all the way to the bottom by
  shortening it to accommodate the mobile-topbar.

- Make the item name in the mobile-topbar clickable to go to the top of
  the page.

- Remove excess padding sidebar in mobile mode.

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

@@ -72,7 +72,7 @@ function resourcePath(basename, extension) {
         var mobileLocationTitle = document.querySelector(".mobile-topbar h2.location");
         var locationTitle = document.querySelector(".sidebar h2.location");
         if (mobileLocationTitle && locationTitle) {
-            mobileLocationTitle.innerText = locationTitle.innerText;
+            mobileLocationTitle.innerHTML = locationTitle.innerHTML;
         }
     }
 }());