fix(sveltekit): Avoid data invalidation in wrapped client-side load functions

[Lms24]

This PR fixes a data invalidation issue that appeared on the client side when auto-instrumenting or manually wrapping universal load functions. Because our wrapLoadWithSentry function accessed event.route.id, the data returned from load would be invalidated on a route change. As reported in #8818 , this caused prefetched, actually valid data to be invalidated during the navigation to the page, causing another load invocation.

To avoid this invalidation, we change the way how we read the route.id, to first use Object.getOwnPropertyDescriptor which doesn't trigger the proxy that listens to accesses. This, however, will only work for @sveltejs/kit>=1.24.0 which includes a change to the Kit-internal proxy. For older versions of kit, we continue to directly read from event.route.id, which will still cause invalidations. Not ideal but IMO the best we can do without loosing data.

I'll open a separate PR to docs, recommending to use the SDK with Kit 1.24.0 or newer (but 1.0.0 will still be the minimal supported version).

closes #8818