fix: load the URL shown in the address bar when returning to a pushState/replaceState history entry

[Nic-Polumeyv]

closes #11465

pushState and replaceState write one URL to the address bar and store a different one in the history entry:

const opts = {
	[HISTORY_INDEX]: (current_history_index += 1),
	[NAVIGATION_INDEX]: current_navigation_index,
	[PAGE_URL_KEY]: page.url.href, // the page we were on
	[STATES_KEY]: state
};

history.pushState(opts, '', resolve_url(url)); // the URL the user sees

When you later return to that entry, the popstate handler feeds PAGE_URL_KEY to navigate, so load runs with the old URL while the address bar shows the pushed one. That's the report in the issue, url.searchParams in load missing params that are visibly in the URL after going back.

Both functions now store the same resolved URL they push. This follows teemingc's comment on the issue, keep the page store URL at push time but update the URL that subsequent loads run with.

One existing assertion changes. "Replaces state on a new URL" expected that going forward to a replaced entry renders the old page under the new URL, which is the inconsistency being fixed. It now expects the route the address bar shows, with page.state still restored. A new test covers the reported sequence, push, navigate away, go back, and fails on main.

This doesn't touch the invalidate-after-pushState case from #11503. That needs a decision on push-time load semantics, and an existing test ("Invalidates the correct route after pushing state to a new URL") deliberately locks in the current behavior, so I left it alone. Happy to take it as a follow-up if there's an agreed direction.

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[pkg-svelte-dev]

Install the latest version of @sveltejs/kit from a7e5b7d:

pnpm add https://pkg.svelte.dev/@sveltejs/kit/c/a7e5b7dede267833dde3cceac18e808d1cb180e3

Open in pkg.svelte.dev: https://pkg.svelte.dev/repos/kit/pr/16307

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