MDL-78885 comboboxsearch: Improve user search and keyboard handling

- Prevent rerendering of the menu when it's already open to preserve the
  selected/highlighted option.
- Allow ArrowUp and ArrowDown to trigger the user search dropdown for
  improved keyboard navigation.

This commit ensures that the menu is not re-rendered when it's already
open, preserving the selected option to enhance the user experience.
Additionally, ArrowUp and ArrowDown keys now trigger the dropdown,
improving keyboard navigation and user interactions.

lib/amd/src/comboboxsearch/search_combobox.js

@@ -352,7 +352,11 @@ export default class {
             this.searchInput.removeAttribute('aria-activedescendant');
         }
         // User may have accidentally clicked off the dropdown and wants to reopen it.
-        if (e.target.closest(this.selectors.input) && this.getSearchTerm() !== '') {
+        if (
+            this.getSearchTerm() !== ''
+            && !this.getHTMLElements().searchDropdown.classList.contains('show')
+            && e.target.closest(this.selectors.input)
+        ) {
             await this.renderAndShow();
         }
     }