[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;
+  }
+}