Add `onDone` or `onClose` or something, just to allow to do some clean up after the analyzer done processing

**Description:**
Like we have the `createPlugin` entryPoint we need another function that allow us to do some clean up after the analyzer finish his job


```dart
// This is the entrypoint of our custom linter
PluginBase createPlugin() => _ExampleLinter();

// This should be called after the analyzer done
void onDone() {
//Doing some clean up here.
};

```

