UX: Resize dmenu width for filter on window resize (#34091)

Since we don't have native floatkit/dmenu functionality (yet) to
make the menu stick to the width of the element, this is a
stopgap solution to make sure the menu stays the same width
as the filter input whether resizing the window or hiding/showing
the menu.

app/assets/javascripts/discourse/app/components/discovery/filter-navigation-menu.gjs

@@ -15,6 +15,7 @@ import concatClass from "discourse/helpers/concat-class";
 import icon from "discourse/helpers/d-icon";
 import withEventValue from "discourse/helpers/with-event-value";
 import discourseDebounce from "discourse/lib/debounce";
+import { bind } from "discourse/lib/decorators";
 import FilterSuggestions from "discourse/lib/filter-suggestions";
 import { resettableTracked } from "discourse/lib/tracked-tools";
 import { i18n } from "discourse-i18n";
@@ -86,6 +87,16 @@ export default class FilterNavigationMenu extends Component {
 
   @tracked _selectedIndex = -1;
 
+  constructor() {
+    super(...arguments);
+    window.addEventListener("resize", this.resizeDMenu);
+  }
+
+  willDestroy() {
+    super.willDestroy(...arguments);
+    window.removeEventListener("resize", this.resizeDMenu);
+  }
+
   get selectedIndex() {
     return this._selectedIndex;
   }
@@ -377,6 +388,12 @@ export default class FilterNavigationMenu extends Component {
   async openFilterMenu() {
     if (this.dMenuInstance) {
       this.dMenuInstance.show();
+
+      // HACK: We don't have a nice way for DMenu to be the same width as
+      // the input element, so we set it manually.
+      schedule("afterRender", () => {
+        this.resizeDMenu();
+      });
       return;
     }
 
@@ -390,13 +407,22 @@ export default class FilterNavigationMenu extends Component {
     // HACK: We don't have a nice way for DMenu to be the same width as
     // the input element, so we set it manually.
     schedule("afterRender", () => {
-      if (this.dMenuInstance?.content) {
-        this.dMenuInstance.content.style.width =
-          this.inputElement.offsetWidth + "px";
-      }
+      this.resizeDMenu();
     });
   }
 
+  @bind
+  resizeDMenu() {
+    if (!this.inputElement || !this.dMenuInstance) {
+      return;
+    }
+
+    if (this.dMenuInstance.content) {
+      this.dMenuInstance.content.style.width =
+        this.inputElement.offsetWidth + "px";
+    }
+  }
+
   @action
   handleKeydown(event) {
     if (