src/vs/platform/extensionManagement/common/extensionStorage.ts/ExtensionStorageService/getSourceExtensionToMigrate
class ExtensionStorageService:	getSourceExtensionToMigrate(toExtensionId: string): string | undefined {
		const entry = this.migrationList.find(([, to]) => toExtensionId === to);
		return entry ? entry[0] : undefined;
	}