[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/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",