ui: add complex descriptors selection in problem search (#636)

Co-authored-by: undefined <i@undefined.moe>
Co-authored-by: panda <panda_dtdyy@outlook.com>

packages/ui-default/templates/problem_main.html

@@ -15,6 +15,11 @@
               </button>
             </div>
           </form>
+        </div>
+        {% if handler.domain.pinnedFilter %}
+          {% include "partials/problem_search.html" %}
+        {% endif %}
+        <div class="section__body no-padding">
           {% include "partials/problem_list.html" %}
         </div>
       </div>