refactor(shared-docs): make the SearchItem directive OnPush compatible (

#2072)

The SearchItem directive has a local state (isActive) used in a host binding.
Prior to this change the state was updated from a method call without marking
the corresponding view for check. This meant that the directive in question
could not be used in an OnPush component as the directive's host bindings
would not be re-evaluated.

PR Close #2072

docs/directives/search-item/search-item.directive.ts

@@ -6,7 +6,7 @@
  * found in the LICENSE file at https://angular.dev/license
  */
 
-import {Directive, ElementRef, Input, inject} from '@angular/core';
+import {Directive, ElementRef, Input, inject, signal} from '@angular/core';
 import {Highlightable} from '@angular/cdk/a11y';
 import {SearchResult} from '../../interfaces/search-results';
 
@@ -23,18 +23,18 @@ export class SearchItem implements Highlightable {
 
   private readonly elementRef = inject(ElementRef<HTMLLIElement>);
 
-  private _isActive = false;
+  private _isActive = signal(false);
 
   protected get isActive() {
-    return this._isActive;
+    return this._isActive();
   }
 
   setActiveStyles(): void {
-    this._isActive = true;
+    this._isActive.set(true);
   }
 
   setInactiveStyles(): void {
-    this._isActive = false;
+    this._isActive.set(false);
   }
 
   getLabel(): string {