src/vs/platform/configuration/common/configuration.ts/getMigratedSettingValue
export function getMigratedSettingValue<T>(configurationService: IConfigurationService, currentSettingName: string, legacySettingName: string): T {
	const setting = configurationService.inspect<T>(currentSettingName);
	const legacySetting = configurationService.inspect<T>(legacySettingName);

	if (typeof setting.userValue !== 'undefined' || typeof setting.workspaceValue !== 'undefined' || typeof setting.workspaceFolderValue !== 'undefined') {
		return setting.value!;
	} else if (typeof legacySetting.userValue !== 'undefined' || typeof legacySetting.workspaceValue !== 'undefined' || typeof legacySetting.workspaceFolderValue !== 'undefined') {
		return legacySetting.value!;
	} else {
		return setting.defaultValue!;
	}
}