Add SvelteKit client-side error monitoring instrumentation

[Lms24]

To get error monitoring for the client-side of SvelteKit apps, we need to ensure that all errors are caught:

To wrap the handleError hook, I already created a PoC that we can probably base our implementation on. For now it's enough to export this wrapper to let users add it manually. Later on, we can add auto-wrapping functionality like in NextJS.

### Tasks
- [ ] https://github.com/getsentry/sentry-javascript/pull/7406
- [x] Ensure default integrations capture errors not caught by the `handleError` hook
- [x] [Needs Research] Should we Instrument [`+error.svelte`](https://kit.svelte.dev/docs/routing#error) pages?

[AbhiPrasad]

I did some testing with Ensure default integrations capture errors not caught by the handleError hook, and since we have functionality in the SDK to avoid double capturing the same error, it seems this should be fine.

[AbhiPrasad]

Re: the Should we Instrument +error.svelte pages? task, I asked about this here, and from testing internally it might be too noisy. What we probably want to do is only wrap the server-side error helper. Will update #7403 accordingly.