eslint: Fix unicorn/{new-for-builtins,throw-new-error,error-message}.

https://github.com/sindresorhus/eslint-plugin-unicorn/blob/master/docs/rules/new-for-builtins.md
https://github.com/sindresorhus/eslint-plugin-unicorn/blob/master/docs/rules/throw-new-error.md
https://github.com/sindresorhus/eslint-plugin-unicorn/blob/master/docs/rules/error-message.md

Signed-off-by: Anders Kaseorg <anders@zulip.com>

frontend_tests/node_tests/keydown_util.js

@@ -10,7 +10,7 @@ run_test("test_early_returns", () => {
         elem: stub,
         handlers: {
             left_arrow: () => {
-                throw Error("do not dispatch this with alt key");
+                throw new Error("do not dispatch this with alt key");
             },
         },
     };