feat(aria/tree): Extend public api with expansion methods

Author: adolgachev

src/aria/tree/tree.ts

@@ -205,6 +205,16 @@ export class Tree<V> {
   scrollActiveItemIntoView(options: ScrollIntoViewOptions = {block: 'nearest'}) {
     this._pattern.inputs.activeItem()?.element().scrollIntoView(options);
   }
+
+  /** Expands all tree items if multi-expandable. */
+  expandAll() {
+    this._pattern.expansionManager.openAll();
+  }
+
+  /** Collapses all tree items. */
+  collapseAll() {
+    this._pattern.expansionManager.closeAll();
+  }
 }
 
 /**