src/vs/base/browser/ui/list/listWidget.ts/List/focusNext
class List:	focusNext(n = 1, loop = false, browserEvent?: UIEvent, filter?: (element: T) => boolean): void {
		if (this.length === 0) { return; }

		const focus = this.focus.get();
		const index = this.findNextIndex(focus.length > 0 ? focus[0] + n : 0, loop, filter);

		if (index > -1) {
			this.setFocus([index], browserEvent);
		}
	}