core(fr): use frame url in gather context

[adamraine]

In legacy navigations context.url is the current frame URL and is unaffected by the history API.

However in FR navigations, context.url is the result of page.url() from Puppeteer and is affected by the history API. This can lead to issues in FR navigations where we try and use context.url to get the main document, but context.url is not the URL used to fetch the main document.

This PR ensures context.url reflects the current frame URL without considering any history API calls once we reach the getArtifact phase.

---

Once we deprecate the legacy navigation runner, I think we should deprecate context.url. Then we can use context.baseArtifacts.URL to get the frame URL and context.driver.url() to get the URL affected by history API.