Move Jest config from package.json to jest.config.js (#5680)

Having this config outside of package.json is consistent with the rest
of our configurations. It also lets us add comments.

And it will make it easier to add other test environments, for example
if we want to test how code runs in a pure node environment rather than
in the browser-like environment.

Author: mstange

jest.config.js

@@ -0,0 +1,40 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+module.exports = {
+  testMatch: ['<rootDir>/src/**/*.test.{js,jsx,ts,tsx}'],
+  moduleFileExtensions: ['js', 'jsx', 'ts', 'tsx'],
+
+  testEnvironment: './src/test/custom-environment',
+  setupFilesAfterEnv: ['jest-extended/all', './src/test/setup.ts'],
+
+  collectCoverageFrom: [
+    'src/**/*.{js,jsx,ts,tsx}',
+    '!**/node_modules/**',
+    '!src/types/libdef/**',
+  ],
+
+  // Transform ESM modules to CommonJS for Jest
+  // These packages ship as pure ESM and need to be transformed by Babel
+  transformIgnorePatterns: [
+    '/node_modules/(?!(query-string|decode-uri-component|iongraph-web|split-on-first|filter-obj|fetch-mock)/)',
+  ],
+
+  // Mock static assets (images, CSS, etc.)
+  moduleNameMapper: {
+    '\\.(jpg|jpeg|png|gif|eot|otf|webp|svg|ttf|woff|woff2|mp4|webm|wav|mp3|m4a|aac|oga|ftl)$':
+      '<rootDir>/src/test/fixtures/mocks/file-mock.ts',
+    '\\.(css|less)$': '<rootDir>/src/test/fixtures/mocks/style-mock.ts',
+  },
+
+  globals: {
+    AVAILABLE_STAGING_LOCALES: null,
+  },
+
+  snapshotFormat: {
+    escapeString: true,
+    printBasicPrototype: true,
+  },
+  verbose: false,
+};

package.json

@@ -194,39 +194,6 @@
     "@types/react-splitter-layout/@types/react": "^18.3.26",
     "@types/trusted-types": "^2.0.7"
   },
-  "jest": {
-    "collectCoverageFrom": [
-      "src/**/*.{js,jsx,ts,tsx}",
-      "!**/node_modules/**",
-      "!src/types/libdef/**"
-    ],
-    "moduleFileExtensions": [
-      "js",
-      "jsx",
-      "ts",
-      "tsx"
-    ],
-    "transformIgnorePatterns": [
-      "/node_modules/(?!(query-string|decode-uri-component|iongraph-web|split-on-first|filter-obj|fetch-mock)/)"
-    ],
-    "moduleNameMapper": {
-      "\\.(jpg|jpeg|png|gif|eot|otf|webp|svg|ttf|woff|woff2|mp4|webm|wav|mp3|m4a|aac|oga|ftl)$": "<rootDir>/src/test/fixtures/mocks/file-mock.ts",
-      "\\.(css|less)$": "<rootDir>/src/test/fixtures/mocks/style-mock.ts"
-    },
-    "setupFilesAfterEnv": [
-      "jest-extended/all",
-      "./src/test/setup.ts"
-    ],
-    "globals": {
-      "AVAILABLE_STAGING_LOCALES": null
-    },
-    "snapshotFormat": {
-      "escapeString": true,
-      "printBasicPrototype": true
-    },
-    "testEnvironment": "./src/test/custom-environment",
-    "verbose": false
-  },
   "husky": {
     "hooks": {
       "post-checkout": "node bin/post-checkout.js",