Automatically render wiki TOC (#19873)

Automatically add sidebar in the wiki view containing a TOC for the wiki page.
Make the TOC collapsable

Signed-off-by: Andrew Thornton <art27@cantab.net>

web_src/less/_repository.less

@@ -3088,6 +3088,18 @@ td.blob-excerpt {
   }
 }
 
+.wiki-content-toc {
+  > ul > li {
+    margin-bottom: 4px;
+  }
+
+  ul {
+    margin: 0;
+    list-style: none;
+    padding-left: 1em;
+  }
+}
+
 /* fomantic's last-child selector does not work with hidden last child */
 .ui.buttons .unescape-button {
   border-top-right-radius: .28571429rem;