update(zoom): set store instance before emitting pane-ready event

* add missing generics on getters
* replace ? notation with undefined (does not mean the exact same, i.e.
`instance?: FlowInstance` will become `Ref<FlowInstance | undefined> | undefined`
using `instance: FlowInstance | undefined` results in `Ref<FlowInstance | undefined>`

Signed-off-by: Braks <78412429+bcakmakoglu@users.noreply.github.com>

src/types/flow.ts

@@ -179,5 +179,5 @@ export type UseVueFlow<N = any, E = N> = {
   store: FlowStore<N, E>
 } & FlowHooksOn<N, E> &
   ToRefs<State<N, E>> &
-  Getters &
+  Getters<N, E> &
   Actions<N, E>