* Reimplement @urql/svelte bindings with new API approach

* Accept only stores as input in query/subscription

When GraphQLRequest is passed this is usually fine, but when
the operation is then instantiated multiple times per component
lifecycle, this causes a memory leak of multiple active subscriptions
until the component unmounts.
This can simply be discouraged by requiring the store.

* Readd @urql/core re-export

* Fix set in development and allow empty updates

* Move context options to operationStore

* Update operationStore to simplify defineProperty calls

* Add tests for operationStore

* Add tests for query and subscription operations

* Add tests for mutation operation

* Add forced update due to changed context

* Simplify invalidate logic in operationStore

* Fix how getters are defined to work around broken minification

* Add Svelte docs sections to guide pages

* Add Svelte API docs

* Add changeset

* Fix Svelte API docs title

* Rename noop variable