fix(codegen): document.documentElement is null on early navigation

[mxschmitt]

This PR fixes the following when opening Codegen on https://primevue.org/inputnumber/:

VM26:921 Recorder::installListners install error TypeError: Cannot read properties of null (reading 'contains')
    at Highlight.install (<anonymous>:4742:56)
    at Recorder.installListeners (eval at extend (inputnumber/:5876:40), <anonymous>:919:22)
    at new Recorder (eval at extend (inputnumber/:5876:40), <anonymous>:890:10)
    at new PollingRecorder (eval at extend (inputnumber/:5876:40), <anonymous>:1322:22)
    at InjectedScript.extend (<anonymous>:5882:12)
    at eval (eval at evaluate (inputnumber/:234:30), <anonymous>:5:29)
    at UtilityScript.evaluate (<anonymous>:236:17)
    at UtilityScript.<anonymous> (<anonymous>:1:44)

In TypeScript this type is not nullable. This is working as intended from their side: microsoft/TypeScript#50078

Minimal Playwright repro script. This sometimes returns true and sometimes false.

import { chromium } from 'playwright';

(async () => {
  const check = async () => {
    const browser = await chromium.launch({ headless: false });
    const context = await browser.newContext();
    const page = await context.newPage();
    await page.goto('https://primevue.org/inputnumber/', {waitUntil: 'commit'});
    console.log(await page.evaluate(() => !!document.documentElement));

    await context.close();
    await browser.close();
  };
  while (true)
    await check();
})();

Contract-wise we have three users of Highlight::install:

1. Recorder.installListeners
2. Locator.highlight
3. Locator.maskSelectors

The first one retries every couple of seconds. The other two we expect to be called after the navigation has happened IIUC.

I went over the rest of the code-base, there we usually check for null when interacting with document.documentElement.

[github-actions]

Test results for "tests 1"

3 flaky

⚠️ [chromium-page] › page/page-event-request.spec.ts:138:3 › should report navigation requests and responses handled by service worker with routing @chromium-ubuntu-22.04-node18
⚠️ [chromium-page] › page/page-event-request.spec.ts:110:3 › should report navigation requests and responses handled by service worker @chromium-ubuntu-22.04-node22
⚠️ [chromium-library] › library/inspector/cli-codegen-java.spec.ts:49:5 › should print the correct context options when using a device @ubuntu-20.04-chromium-tip-of-tree

36892 passed, 650 skipped
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Merge workflow run.