src/vs/workbench/api/common/extHostTreeViews.ts/ExtHostTreeView/setExpanded
class ExtHostTreeView:	setExpanded(treeItemHandle: TreeItemHandle, expanded: boolean): void {
		const element = this.getExtensionElement(treeItemHandle);
		if (element) {
			if (expanded) {
				this._onDidExpandElement.fire(Object.freeze({ element }));
			} else {
				this._onDidCollapseElement.fire(Object.freeze({ element }));
			}
		}
	}