feat: Add loading indicator slot and prop

* While the graph is suspended we open up a loading indicator slot
* a prop option has to be passed to enable the indicator
* add some styles for a default loading text
* move loading event to after store has been initialized *and* zoom pane dimensions are present

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

src/store/stateStore.ts

@@ -64,8 +64,8 @@ export default function flowStore(
           workerTerminate('SUCCESS')
         }
         this.elements = elements
-        this.nodes = next.nextNodes
-        this.edges = next.nextEdges
+        this.nodes = next?.nextNodes ?? []
+        this.edges = next?.nextEdges ?? []
       },
       updateNodeDimensions({ id, nodeElement, forceUpdate }) {
         const i = this.nodes.map((x) => x.id).indexOf(id)

src/store/utils.ts

@@ -88,8 +88,7 @@ export const initialState = (): FlowState => ({
 
   isReady: false,
   hooks: createHooks(),
-  storageKey: undefined,
-  instance: undefined,
+  showLoadingIndicator: false,
 
   vueFlowVersion: typeof __VUE_FLOW_VERSION__ !== 'undefined' ? __VUE_FLOW_VERSION__ : '-',
 })