fix: correctly handle HttpError on the client

[gtm-nayan]

Closes #7966
Closes #8142

Reading this comment, there's a chance I may have completely misunderstood what the PR was trying to do, but at least this is what I got from the repro and the list of steps on #7966.

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[dummdidumm]

The problem I tried to articulate there is that if you throw an error from the handle hook, there's nothing to fall back to. The handle hook is "above" the root layout, which means we need to fall back to the static error page (which you can customize through error.html). That happens when hitting the server directly already, but for the client there's no good way to do that currently: If the error is thrown from a __data.json request, we can't magically transform that response into the static error page. We can't just show the root layout and its error page either, because the root layout might fire off another __data.json request, which results in another error thrown in the handle hook.

[gtm-nayan]

Trying to wrap my head around it, but feels like that probably warrants a separate discussion, this change still addresses #7966 right?

[dummdidumm]

Sort of - if you have a +layout.server.js in your root, that request will still be done when falling back to the root error page with the root layout, which triggers another handle hook invocation. This will probably trigger a full reload and that will show the static error page, but if you're in SPA mode then it won't I think.

This PR makes sense to me in either way because the unexpected error which is thrown while request __data.json should've been handled by the server and its handleError already, so it shouldn't result in another client handleError invocation.