src/vs/editor/contrib/documentSymbols/browser/outlineModel.ts/TreeElement/getElementById
class TreeElement:	static getElementById(id: string, element: TreeElement): TreeElement | undefined {
		if (!id) {
			return undefined;
		}
		let len = commonPrefixLength(id, element.id);
		if (len === id.length) {
			return element;
		}
		if (len < element.id.length) {
			return undefined;
		}
		for (const [, child] of element.children) {
			let candidate = TreeElement.getElementById(id, child);
			if (candidate) {
				return candidate;
			}
		}
		return undefined;
	}