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

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

@@ -0,0 +1,10 @@
+import { Stream } from "./Stream";
+/** @interface */
+export interface Encoder {
+    /**
+     * @param {Stream} stream The stream of code points being encoded.
+     * @param {number} code_point Next code point read from the stream.
+     * @return {(number|!Array.<number>)} Byte(s) to emit, or |finished|.
+     */
+    handler(stream: Stream, code_point: number): number | number[];
+}