[dashboard] fix Reset dashboard breaks panel state when ran after edi…

…tor edits (elastic#201687)

Closes elastic#201627

### The problem
`ReactEmbeddableRender` uses `lastSavedRuntimeState` as last saved state
baseline. Resetting reverts to this state.
```
// Code sample from src/plugins/embeddable/public/react_embeddable_system/react_embeddable_renderer.tsx
const serializedState = parentApi.getSerializedStateForChild(uuid);
const lastSavedRuntimeState = serializedState
  ? await factory.deserializeState(serializedState)
  : ({} as RuntimeState);

...

const unsavedChanges = initializeUnsavedChanges<RuntimeState>(
  lastSavedRuntimeState,
  parentApi,
  comparators
);
```

`DashboardContainer` getSerializedStateForChild implemenation
```
// Code sample from src/plugins/dashboard/public/dashboard_container/embeddable/dashboard_container.tsx
public getSerializedStateForChild = (childId: string) => {
    const rawState = this.getInput().panels[childId].explicitInput;
    const { id, ...serializedState } = rawState;
    if (!rawState || Object.keys(serializedState).length === 0) return;
    const references = getReferencesForPanelId(childId, this.savedObjectReferences);
    return {
      rawState,
      // references from old installations may not be prefixed with panel id
      // fall back to passing all references in these cases to preserve backwards compatability
      references: references.length > 0 ? references : this.savedObjectReferences,
    };
  };
```

The problem is that `create_dashboard` clears
`this.getInput().panels[childId].explicitInput` for a panel with
embeddable transfer state. This causes `lastSavedRuntimeState` to be an
empty object, which causes reset to use `undefined` for the previous
value when reseting an embeddables keys.
```
// Code sample from src/plugins/dashboard/public/dashboard_container/embeddable/create/create_dashboard.ts
const incomingEmbeddable = creationOptions?.getIncomingEmbeddable?.();
if (
  incomingEmbeddable.embeddableId &&
  Boolean(initialDashboardInput.panels[incomingEmbeddable.embeddableId])
) {
  // this embeddable already exists, we will update the explicit input.
  const panelToUpdate = initialDashboardInput.panels[incomingEmbeddable.embeddableId];
  const sameType = panelToUpdate.type === incomingEmbeddable.type;

  panelToUpdate.type = incomingEmbeddable.type;
  const nextRuntimeState = {
    // if the incoming panel is the same type as what was there before we can safely spread the old panel's explicit input
    ...(sameType ? panelToUpdate.explicitInput : {}),

    ...incomingEmbeddable.input,
    id: incomingEmbeddable.embeddableId,

    // maintain hide panel titles setting.
    hidePanelTitles: panelToUpdate.explicitInput.hidePanelTitles,
  };
  if (embeddableService.reactEmbeddableRegistryHasKey(incomingEmbeddable.type)) {
    panelToUpdate.explicitInput = { id: panelToUpdate.explicitInput.id };
    runtimePanelsToRestore[incomingEmbeddable.embeddableId] = nextRuntimeState;
  } else {
    panelToUpdate.explicitInput = nextRuntimeState;
  }
}
```

### The fix
The solution is to retain `panelToUpdate.explicitInput` original value
so that `lastSavedRuntimeState` is set to the original runtime state and
reset will revert to this value instead of `{}`.

### test instructions
1) install web logs sample data
2) create new dashboard
3) click "Add panel" and select "Legacy => Agg based"
4) create pie chart with terms split on "machine.os", click "Save and
return"
5) save dashboard
6) edit pie chart, Under "options", unselect "donut". Click "Save and
return"
7) click reset in dashboard. Verify that visualization returns to
original state. Note, the same will not happen for map embeddables.
There is a bug in map embeddables where resetting "attributes" state
does not update the current map.

Co-authored-by: Elastic Machine <[email protected]>

src/plugins/dashboard/public/dashboard_container/embeddable/create/create_dashboard.ts

@@ -362,7 +362,6 @@ export const initializeDashboard = async ({
         hidePanelTitles: panelToUpdate.explicitInput.hidePanelTitles,
       };
       if (embeddableService.reactEmbeddableRegistryHasKey(incomingEmbeddable.type)) {
-        panelToUpdate.explicitInput = { id: panelToUpdate.explicitInput.id };
         runtimePanelsToRestore[incomingEmbeddable.embeddableId] = nextRuntimeState;
       } else {
         panelToUpdate.explicitInput = nextRuntimeState;