Fix auto-hide for implementations and implementors.

This sets their toggles to be closed in the HTML (matching the default
setting), and opens them if the setting indicates to do so.

This distinguishes between implementations and implementors based on
being descendants of certain named elements.

src/librustdoc/html/render/mod.rs

@@ -1545,7 +1545,7 @@ fn render_impl(
     let open_details = |close_tags: &mut String| {
         if toggled {
             close_tags.insert_str(0, "</details>");
-            "<details class=\"rustdoc-toggle implementors-toggle\" open><summary>"
+            "<details class=\"rustdoc-toggle implementors-toggle\"><summary>"
         } else {
             ""
         }