Add barcode-detector-api-polyfill dependency and update environment variable declarations in SvelteKit project

node_modules/@zxing/text-encoding/es2015/common/Decoder.d.ts

@@ -0,0 +1,12 @@
+import { Stream } from "./Stream";
+/** @interface */
+export interface Decoder {
+    /**
+     * @param {Stream} stream The stream of bytes being decoded.
+     * @param {number} bite The next byte read from the stream.
+     * @return {?(number|!Array.<number>)} The next code point(s)
+     *     decoded, or null if not enough data exists in the input
+     *     stream to decode a complete code point, or |finished|.
+     */
+    handler(stream: Stream, bite: number): number | number[];
+}