src/vs/workbench/common/configuration.ts/ConfigurationMigrationWorkbenchContribution/migrateConfigurationForFolderOverrideAndTarget
class ConfigurationMigrationWorkbenchContribution:	private async migrateConfigurationForFolderOverrideAndTarget(migration: ConfigurationMigration, overrides: IConfigurationOverrides, data: IConfigurationValue<any>, dataKey: keyof IConfigurationValue<any>, target: ConfigurationTarget): Promise<void> {
		const value = data[dataKey];
		if (typeof value === 'undefined') {
			return;
		}

		const valueAccessor = (key: string) => this.configurationService.inspect(key, overrides)[dataKey];
		const result = await migration.migrateFn(value, valueAccessor);
		const keyValuePairs: ConfigurationKeyValuePairs = Array.isArray(result) ? result : [[migration.key, result]];
		await Promise.allSettled(keyValuePairs.map(async ([key, value]) => this.configurationService.updateValue(key, value.value, overrides, target)));
	}