SvelteKIT: Support ESM for Vitest test runs

code/frameworks/sveltekit/src/plugins/mock-sveltekit-stores.ts

@@ -1,16 +1,21 @@
-import { resolve } from 'node:path';
+import { dirname, resolve } from 'node:path';
+import { fileURLToPath } from 'node:url';
 
 import type { Plugin } from 'vite';
 
+// @ts-expect-error We are building for CJS and ESM, so we have to use import.meta.url for the ESM output
+const filename = __filename ?? fileURLToPath(import.meta.url);
+const dir = dirname(filename);
+
 export async function mockSveltekitStores() {
   return {
     name: 'storybook:sveltekit-mock-stores',
     config: () => ({
       resolve: {
         alias: {
-          '$app/forms': resolve(__dirname, '../src/mocks/app/forms.ts'),
-          '$app/navigation': resolve(__dirname, '../src/mocks/app/navigation.ts'),
-          '$app/stores': resolve(__dirname, '../src/mocks/app/stores.ts'),
+          '$app/forms': resolve(dir, '../src/mocks/app/forms.ts'),
+          '$app/navigation': resolve(dir, '../src/mocks/app/navigation.ts'),
+          '$app/stores': resolve(dir, '../src/mocks/app/stores.ts'),
         },
       },
     }),