Upgrade to ESLint 9 (#1149)

* Upgrade to eslint 9

* Fix version numbers in package.json files

eslint.config.js

@@ -0,0 +1,73 @@
+const js = require('@eslint/js');
+const globals = require('globals');
+
+const prettier = require('eslint-plugin-prettier');
+const eslintPluginPrettierRecommended = require('eslint-plugin-prettier/recommended');
+
+const jest = require('eslint-plugin-jest');
+
+module.exports = [
+  js.configs.recommended,
+  eslintPluginPrettierRecommended,
+  {
+    plugins: {
+      prettier
+    },
+    rules: {
+      'prettier/prettier': ['error'],
+      'no-var': ['error'],
+      'no-unused-vars': [
+        'warn',
+        {
+          argsIgnorePattern: '^_',
+          varsIgnorePattern: '^_'
+        }
+      ]
+    },
+    languageOptions: {
+      ecmaVersion: 'latest',
+      sourceType: 'module',
+      globals: {
+        ...globals.browser,
+        ...globals.webextensions,
+        ...globals.es2021,
+        ...globals.jquery,
+        ...globals.serviceworker
+      }
+    }
+  },
+  {
+    files: [
+      'functional-samples/tutorial.puppeteer/**/*',
+      'functional-samples/tutorial.terminate-sw/**/*'
+    ],
+    plugins: { jest },
+    rules: {
+      ...jest.configs['flat/recommended'].rules
+    },
+    languageOptions: {
+      globals: {
+        ...globals.jest
+      }
+    },
+    settings: {
+      jest: {
+        version: '29.7.0'
+      }
+    }
+  },
+  {
+    // Ignores must be in a separate block to apply globally:
+    // https://eslint.org/docs/latest/use/configure/configuration-files#globally-ignoring-files-with-ignores
+    ignores: [
+      'eslint.config.js',
+      '.repo/**/*',
+      '_archive/**/*',
+      '**/third-party/**',
+      '**/node_modules/**/*',
+      // These are autogenerated files that we shouldn't lint
+      'functional-samples/cookbook.wasm-helloworld-print/wasm/pkg/**/*',
+      'functional-samples/cookbook.wasm-helloworld-print-nomodule/wasm/pkg/**/*'
+    ]
+  }
+];