src/vs/base/browser/ui/iconLabel/iconLabelHover.ts/getTooltipForCustom
function getTooltipForCustom(markdownTooltip: string | IIconLabelMarkdownString): (token: CancellationToken) => Promise<string | IMarkdownString | undefined> {
	if (isString(markdownTooltip)) {
		return async () => markdownTooltip;
	} else if (isFunction(markdownTooltip.markdown)) {
		return markdownTooltip.markdown;
	} else {
		const markdown = markdownTooltip.markdown;
		return async () => markdown;
	}
}