src/vs/platform/userDataSync/common/settingsMerge.ts/addSetting
export function addSetting(key: string, sourceContent: string, targetContent: string, formattingOptions: FormattingOptions): string {
	const source = parse(sourceContent);
	const sourceTree = parseSettings(sourceContent);
	const targetTree = parseSettings(targetContent);
	const insertLocation = getInsertLocation(key, sourceTree, targetTree);
	return insertAtLocation(targetContent, key, source[key], insertLocation, targetTree, formattingOptions);
}