[ACA-3899] Viewer thumbnails cannot be accessed by keyboard (#6150)

* accessibility

* add thumb focus

* close thumbs list event

* fix eventbus listener

* rename parameter

* track previous focused element

* implement FocusKeyManager

* fix getGlobalEventBus is deprecated

* keyboard navigation

* set tabindex

* setActiveItem on list change

* update  test

lib/core/viewer/components/pdf-viewer-thumbnails.component.html

@@ -4,6 +4,7 @@
     [style.transform]="'translate(-50%, ' + translateY + 'px)'">
     <adf-pdf-thumb *ngFor="let page of renderItems; trackBy: trackByFn"
         class="adf-pdf-thumbnails__thumb"
+        [id]="page.id"
         [ngClass]="{'adf-pdf-thumbnails__thumb--selected' : isSelected(page.id)}"
         [page]="page"
         (click)="goTo(page.id)">