Messages are not sent when dynamic page cache is active

This one was a bit tricky to fix. For it to work I had to move it to dynamic content and make dynamic content to be fetched later. This seems all fine, but is a rather-big change, thus I'd rather tag it in 2.5.0 and create change notice to communicate.

However, the only thing it could influence is local-task generation, for which I added a test-case, so this is proven to still work.

draft change notice: https://www.drupal.org/node/3526109 →

thank you for the review! Merged and published change record.