Auto merge of #25225 - bluss:doc-search-assoc-items, r=alexcrichton

Rustdoc fixes for associated items

This is related to isssue #22442 and solves it partly.

This solves the search index links of associated types and constants,
so that they link to the trait page.

Also add an Associated Constants section if constants are present.

src/librustdoc/html/static/main.js

@@ -34,7 +34,8 @@
                      "macro",
                      "primitive",
                      "associatedtype",
-                     "constant"];
+                     "constant",
+                     "associatedconstant"];
 
     $('.js-only').removeClass('js-only');