Drop Svelte 3 and 4 Support in `@sentry/svelte` and `@sentry/sveltekit`

[Lms24]

Description

Svelte(kit) deprecated some exports we rely on in our Svelte and SvelteKit SDKs. There are replacements but all of them require Svelte 5. To be able to support the next major version of SvelteKit (not sure when it will arrive), I think we have to drop support for Svelte versions prior to 5 so that we can safely import the new replacement APIs.

Most prominently, this concerns:

import { navigating, page } from '$app/stores'

to be replaced by

import { navigating, page } from '$app/state'

More details: https://svelte.dev/docs/kit/migrating-to-sveltekit-2#SvelteKit-2.12:-$app-stores-deprecated

[linear]

JS-1487