[PM-21934] Upgrade to eslint 9 (#14754)

Upgrades to Eslint v9. Since this is a major version there were breaking changes, but since we've previously migrated to flat configs in #12806 those were minimal.

libs/eslint/fix-jsdom.ts

@@ -0,0 +1,10 @@
+import JSDOMEnvironment from "jest-environment-jsdom";
+
+export default class FixJSDOMEnvironment extends JSDOMEnvironment {
+  constructor(...args: ConstructorParameters<typeof JSDOMEnvironment>) {
+    super(...args);
+
+    // FIXME https://github.com/jsdom/jsdom/issues/3363
+    this.global.structuredClone = structuredClone;
+  }
+}

libs/eslint/jest.config.js

@@ -3,6 +3,7 @@ const sharedConfig = require("../../libs/shared/jest.config.angular");
 /** @type {import('jest').Config} */
 module.exports = {
   ...sharedConfig,
+  testEnvironment: "./fix-jsdom.ts",
   testMatch: ["**/+(*.)+(spec).+(mjs)"],
   displayName: "libs/eslint tests",
   preset: "jest-preset-angular",

libs/eslint/test.setup.mjs

@@ -1,5 +1,3 @@
-/* eslint-disable no-undef */
-
 import { clearImmediate, setImmediate } from "node:timers";
 
 Object.defineProperties(globalThis, {

libs/eslint/tsconfig.json

@@ -1,5 +1,6 @@
 {
   "extends": "../shared/tsconfig",
   "compilerOptions": {},
-  "exclude": ["node_modules", "dist"]
+  "exclude": ["node_modules", "dist"],
+  "files": ["empty.ts"]
 }