/**
 * Ensures the global `Symbol.metadata` well-known symbol exists.
 *
 * The serialization decorator store keys its metadata off `Symbol.metadata`. On a runtime that
 * supports `Symbol` but does not yet expose `Symbol.metadata` natively, the symbol must be created
 * so decorated classes can attach their serialization metadata to their constructor.
 *
 * This module installs the symbol as a one-time, idempotent side effect. Import it for its side
 * effect at package entry points before any decorated class is evaluated.
 */
declare function ApplySymbolMetadataPolyfill(): void;