refactor(types,flow)!: Use reactivity transform and remove store property

# What's changed?

* Remove store property from usevueflow return value
* All previously available properties are still there, just not nested inside an additional store object to avoid confusion + duplicates
* use reactivity transform to get rid of .value calls

package/src/context/index.ts

@@ -1,6 +1,6 @@
 import { InjectionKey, Slots as TSlots } from 'vue'
-import { UseVueFlow } from '~/types'
+import { VueFlowStore } from '~/types'
 
-export const VueFlow: InjectionKey<UseVueFlow> = Symbol('vueFlow')
+export const VueFlow: InjectionKey<VueFlowStore> = Symbol('vueFlow')
 export const NodeId: InjectionKey<string> = Symbol('nodeId')
 export const Slots: InjectionKey<TSlots> = Symbol('slots')