Dashboard entity should support common entity hooks

This might be related to ✨ Dashboards should have the ability to customize path (alias) Postponed and require a meta discussion before implementation.

As you mentioned, dashboards are config entities and we support any config entity hook.
hook_entity_view is a *content* entity hook.
hook_preprocess_HOOK is a theme hook, and we don't provide any specific theme function. Maybe we should, but would still be on the container.

> I need to apply the extra styling via a module and libraries-extend only works for themes.

I'd suggest to attach a library to a block, not the dashboard itself.

If for whatever reason you really need to attach a library to the dashboard itself, and you want to check the id of the dashboard, you can e.g. implement an event subscriber with code like:

  public function onBuildRender(SectionComponentBuildRenderArrayEvent $event) {
    $build = $event->getBuild();
    if (isset($build['#dashboard'])) {
      if ($build['dashboard'] === 'welcome') {
        $build['#attached']['library'][] = 'dashboard_test/test';
       }
    }
    $event->setBuild($build);
  }

  public static function getSubscribedEvents(): array {
    return [
      LayoutBuilderEvents::SECTION_COMPONENT_BUILD_RENDER_ARRAY => [
        'onBuildRender',
      ],
    ];
  }

hook_page_attachments_alter looks to me that another clean solution, but that wouldn't know the actual dashboard.

For the record, for blocks you can do:

function mymodule_preprocess_block(array &$variables): void {
  $dashboard_id = isset($variables['element']['#dashboard']) ?? [];
  if (isset($dashboard_id)) {
     // Do whatever.
  }
}

I've created https://www.drupal.org/docs/extending-drupal/contributed-modules/contrib... →

Let us know if there's something we could document better.