Fix Searchbar dropdown-menu positioning (#2567)

Fix initial dropdown-menu positioning by replacing d-none
with visibility:hidden. Popper.js cannot calculate the position of
elements removed from the DOM with display: none. Let's
replace d-none with visibility:hidden, keeping the element
in the DOM, allowing Popper.js to correctly calculate its position.

packages/vue-components/src/Searchbar.vue

@@ -187,8 +187,8 @@ export default {
       return [
         'dropdown-menu',
         'search-dropdown-menu',
-        { show: this.showDropdown },
-        { 'd-none': !this.showDropdown },
+        { 'show': this.showDropdown },
+        { 'dropdown-menu-hidden': !this.showDropdown },
         { 'dropdown-menu-end': this.menuAlignRight },
       ];
     },
@@ -304,6 +304,10 @@ export default {
         visibility: hidden;
         overflow: hidden;
     }
+
+    .dropdown-menu-hidden {
+        visibility: hidden;
+    }
 </style>
 
 <style>