Problem/Motivation
In the present state of the core inclusion MR, we're missing a way for module authors to mark a Block plugin implementation as 'navigation safe', and listed for use in the Navigation admin UI (/admin/config/user-interface/navigation-block).
Steps to reproduce
As a module author, create a new Block plugin (drush gen module && drush gen block). At this point there should be a way to mark it as 'navigation safe', but there isn't on account of the core navigation module having a static list of approved blocks:
https://git.drupalcode.org/issue/drupal-3438895/-/blob/3438895-add-the-n...
https://git.drupalcode.org/issue/drupal-3438895/-/blob/3438895-add-the-n...
Proposed resolution
Provide a way for module authors to mark block plugins as 'navigation safe'.
Remaining tasks
Review.
User interface changes
None.
API changes
Modules can define their blocks as allowed in navigation in a hook_block_alter() by adding the property allow_in_navigation, like in the MR:
$definition['allow_in_navigation'] = TRUE;
This will be moved to block attributes once #3443882: Allow attribute-based plugins to discover supplemental attributes to set additional properties is merged.
Data model changes
@todo