Remove <QueryClientProvider /> from Svelte adapter

[ottomated]

The current Svelte API feels very React-y. In React, you set context via a provider component and retrieve it via useContext, but in Svelte you set context with the setContext and retrieve it with getContext. Therefore, I propose the following API that feels more Svelte-y:

<script>
  import { QueryClient, setQueryClientContext } from '@tanstack/svelte-query'

  const queryClient = new QueryClient()
  setQueryClientContext(queryClient) // optional, would instantiate a new QueryClient if none is passed
  // or setQueryContext, or setQueryClient
</script>

<Example />

Example.svelte:

<script>
  import { getQueryClient } from '@tanstack/svelte-query'

  const client = getQueryClient();
</script>

This could be an alternate syntax when the Svelte 5 adapter is released and the old syntax could be deprecated slowly and removed in a few major releases from now - both could coexist easily.