add shouldRevalidate export to root loaders

[juanpprieto]

WHY are these changes introduced?

Remix revalidates layouts and routes when the url searchParams are added, removed or changed. This means that all our product page navigations, paginated collection pages and changing product variants were causing the root layout loader to revalidate.

WHAT is this pull request doing?

This PR limits the root loaders to only ever revalidate when a mutation is performed. This includes all cart and account POST/PUT/PATCH requests.

HOW to test your changes?

Console log inside a root loader and navigate into and out of route which include a change in the url. The root loader should only log on first page load and when a mutation e.g add to cart happens.

Checklist

• I've read the Contributing Guidelines
• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've added a changeset if this PR contains user-facing or noteworthy changes

[wizardlyhel]

We don't need the useRevaidator check?

  // user is doing a manual revalidation via useRevalidator
  if (currentUrl.toString() === nextUrl.toString()) {
    return true;
  }

[juanpprieto]

We don't need the useRevaidator check?

  // user is doing a manual revalidation via useRevalidator
  if (currentUrl.toString() === nextUrl.toString()) {
    return true;
  }

Thanks @wizardlyhel. It's back in. I took it out as I was seeing some odd revalidations in the PDP, but triple checked and now they are not happening 🙏🏼