[PP-1] User menu block render array is cached per user

We can close this given that 🐛 Regression: Shortcuts menu flickers when the page is loaded Fixed showed the way to avoid flickering with no need to make an extra effort at render array level.

Same approach could be followed in the future if necessary.

Talked to @mherchel in the weekly Drupal Admin UI call and he also agreed.

   */
  public function build(): array {
    return [
      'user' => [
        '#lazy_builder' => [
          'navigation.user_lazy_builder:renderNavigationLinks',
          [],
        ],
        '#create_placeholder' => TRUE,
        '#cache' => [
          'keys' => ['user_set_navigation_links'],
          'contexts' => ['user'],
        ],
        '#lazy_builder_preview' => [
          '#markup' => '<a href="#" class="toolbar-tray-lazy-placeholder-       link">&nbsp;</a>',
        ],
      ],
    ];
  }

I think there's still an issue here - it now looks like the preview isn't user-specific, but the caching of the preview still is. This could be verified by using the navigation with a couple of different users then checking the cache IDs in the cache_render table.

It could end up being a duplicate of 📌 Investigate using the core "User account menu" in favor of custom Navigation Block for same Active maybe though.

Thank you for the heads up!

Planned to deal with this as part of the mentioned issue 📌 Investigate using the core "User account menu" in favor of custom Navigation Block for same Active once the related issues 📌 Provide a NavigationLinkBlock Plugin and use Help as an usage example Needs review & 📌 Rename UserNavigationBlock to NavigationUserBlock for class name consistency RTBC are in and the ground is ready to mess with it.

We can leave this open as a reference and reminder in the meantime, though.

Postponing on 📌 Provide a NavigationLinkBlock Plugin and use Help as an usage example Needs review (which is really close!!), per last comment by @plopsec.

Updating IS