Bugfix: Incorrect search params stored in cache (#94144)
The route cache write was keying entries on `renderedSearch` — the
search string the server actually used to render the page — but lookups
use the requested URL's search component. These two are not equivalent:
for any search-invariant route (e.g. a static page), `renderedSearch` is
`''` regardless of what the request URL carried.
The result was that a request for `/a?foo=bar` against a static page
parked the cache entry at vary path `(/a, '', null)` — the same slot a
clean `/a` lookup keys to. The entry's stored `canonicalUrl` came from
the requesting URL (`/a?foo=bar`), so a later `router.push('/a')` or
`router.replace('/a')` would hit that slot and restore the stale search
string into the browser address bar, `window.location`, and
`useSearchParams()`.
The fix keys cache writes on the request URL's search, not
`renderedSearch`. Entries now sit at the slot keyed by the request that
wrote them, so a lookup for a different search variant doesn't find
them.
Regression test covers the reproduction from the user repo linked in the
bug reports.
Closes #91658
Closes #92187
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