src/vs/base/browser/ui/menu/menubar.ts/MenuBar/focusNext
class MenuBar:	private focusNext(): void {
		if (!this.focusedMenu || this.numMenusShown === 0) {
			return;
		}

		let newFocusedIndex = (this.focusedMenu.index + 1) % this.numMenusShown;
		if (this.focusedMenu.index === MenuBar.OVERFLOW_INDEX) {
			newFocusedIndex = 0;
		} else if (this.focusedMenu.index === this.numMenusShown - 1) {
			newFocusedIndex = MenuBar.OVERFLOW_INDEX;
		}

		if (newFocusedIndex === this.focusedMenu.index) {
			return;
		}

		if (this.isOpen) {
			this.cleanupCustomMenu();
			this.showCustomMenu(newFocusedIndex);
		} else if (this.isFocused) {
			this.focusedMenu.index = newFocusedIndex;
			if (newFocusedIndex === MenuBar.OVERFLOW_INDEX) {
				this.overflowMenu.buttonElement.focus();
			} else {
				this.menuCache[newFocusedIndex].buttonElement.focus();
			}
		}
	}