feat: add support for using keyword on discord.js Client and WebSocketManager (#10063)

* feat: add support for `using` keyword on client

* fix: use async dispose

* feat: add support for web socket manager disposing

* fix: use interface for client

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Co-authored-by: kodiakhq[bot] <49736102+kodiakhq[bot]@users.noreply.github.com>

packages/util/src/functions/index.ts

@@ -3,3 +3,4 @@ export * from './range.js';
 export * from './calculateShardId.js';
 export * from './runtime.js';
 export * from './userAgentAppendix.js';
+export * from './polyfillDispose.js';

packages/util/src/functions/polyfillDispose.ts

@@ -0,0 +1,14 @@
+/**
+ * Polyfill for `Symbol.dispose` and `Symbol.asyncDispose` which is used as a part of
+ * {@link https://github.com/tc39/proposal-explicit-resource-management}. Node versions below 18.x
+ * don't have these symbols by default, so we need to polyfill them.
+ */
+export function polyfillDispose() {
+	// Polyfill for `Symbol.dispose` and `Symbol.asyncDispose` if not available.
+	// Taken from https://www.typescriptlang.org/docs/handbook/release-notes/typescript-5-2.html#using-declarations-and-explicit-resource-management
+
+	// @ts-expect-error This is a polyfill, so it's fine to write
+	Symbol.dispose ??= Symbol('Symbol.dispose');
+	// @ts-expect-error Same as above
+	Symbol.asyncDispose ??= Symbol('Symbol.asyncDispose');
+}