Make hot reload a standard request

Within the Dart extension, we use a custom request to ask our running application to update source code files that have changed (see https://github.com/Dart-Code/Dart-Code/blob/master/src/extension/dart/hot_reload_save_handler.ts#L116). We’re wondering if this could be made into a standard event type, e.g.:

interface HotReloadRequest extends Request {
  command: 'hotReload';

  arguments: HotReloadArguments;
}

interface HotReloadArguments {
  /** This describes how the hot reload was triggered, e.g. manual request vs automatically on save */
  reason: string;
}

Start with the hot-reload request usage in src/extension/dart/hot_reload_save_handler.ts at line 116, then review the Debug Adapter Protocol request definitions. Determine how the proposed hotReload request and its reason argument fit the protocol, and confirm that the standard request can represent both manual and automatic-on-save reloads.