Define template suggestions available for templates defined by your own module

Documentation to update after we figure this out:

Drupal 8 and 9 core’s Block module uses hook_theme_suggestions_HOOK, where the second “HOOK” is also ‘block’.

The documentation says:

HOOK is the least-specific version of the hook being called. For example, if ‘#theme’ => ’node__article’ is called, then hook_theme_suggestions_node() will be invoked, not hook_theme_suggestions_node__article().

… which means i don’t need any of this, i can stick my suggestion right in the invocation.

I thought it was easy.