src/vs/workbench/api/common/extHostTreeViews.ts/ExtHostTreeView/resolveTreeItem
class ExtHostTreeView:	async resolveTreeItem(treeItemHandle: string, token: vscode.CancellationToken): Promise<ITreeItem | undefined> {
		if (!this.dataProvider.resolveTreeItem) {
			return;
		}
		const element = this.elements.get(treeItemHandle);
		if (element) {
			const node = this.nodes.get(element);
			if (node) {
				const resolve = await this.dataProvider.resolveTreeItem(node.extensionItem, element, token) ?? node.extensionItem;
				// Resolvable elements. Currently only tooltip and command.
				node.item.tooltip = this.getTooltip(resolve.tooltip);
				node.item.command = this.getCommand(node.disposableStore, resolve.command);
				return node.item;
			}
		}
		return;
	}