Add SvelteKit client-side performance monitoring instrumentation

[Lms24]

Having basic error instrumentation, we can move on to performance monitoring.

We're going to add client-side performance monitoring instrumentation:

### Tasks
- [ ] https://github.com/getsentry/sentry-javascript/pull/7447
- [ ] https://github.com/getsentry/sentry-javascript/pull/7528
- [ ] #7565 
- [ ] https://github.com/getsentry/sentry-javascript/pull/7537
- [ ] https://github.com/getsentry/sentry-javascript/pull/7626

For wrapping load and handle functions we should wait for the outcome of the error load wrapper in #7403. Thereafter, we can take my PoC from this discussion as a base: #5838 (reply in thread)

I also started work on a PoC routing instrumentation: https://gist.github.com/Lms24/b36a8f310410240863aa6e50dc19ab3d