Replace drupal_set_message()

Hi nkoporec I reviewed your patch it applies cleanly.

@vakulrai: Thanks for that. However, you should know that a screenshot of you applying a patch doesn't help in any way - we can already tell whether the patch applies based upon the results of the automated tests. What would be useful would be to test a scenario that causes a message to be displayed and then show that the message is still displayed with the new code. Thank you.

The patch applies cleanly and works in that messages are still displayed.

I confirmed these messages still work:
- On install, from drush
- On install, from UI
- Creating new metatag defaults for the article content type on admin/config/search/metatag
- Save message on editing those defaults.
- Deleting those defaults.
- Reverting changes to defaults on 403.

I was not able to get it to display a message after editing the metatags of the admin/content view but I was not able to get the message without the patch, either, so I may be doing it wrong.

I did not test the on translation message as I don't have multi lingual set up on my test site.

Sounds like it works as designed. Thanks Michelle!

Committed. Thank you.

I've reverted this as it breaks compatibility with 8.4, see https://www.drupal.org/node/2774931 for details.

What exactly is this postponed on? Several modules with high installs have already committed similar patches, since Drupal 8.4.x is officially no longer supported. For example:
- Pathauto
- Search API

@idebr: The security team are still releasing security fixes for 8.4.x. Besides, this isn't a bug fix, nothing is broken, it's just some deprecated code so there's no specific hurry on committing it.

I'll reevaluate it after 8.6.0 is released.

I agree with Damien. We just ran into this issue with Paragraphs on a client site. The upgrade path isn't always smooth on these 6 month releases and it can sometimes be tricky to keep up so having an 8.5 requirement in very popular modules means not being able to keep those modules up to date and risking a potential mess if a security release comes out.

Re-rolling the patch as we don't need to use MessengerInterface.
MessengerTrait is available in the parent classes in most cases.

8.4.x is no longer getting security updates, so the time might be right to start replacing this deprecated code.

Agreed.

Reroll against latest 8.x-1.x so it applies cleanly. I did a code review to check all occurrences of drupal_set_message() have been replaced correctly. I will update the status to RTBC when the test comes back green.

Let's add this to the next release.

Ok, *now* it's committed. Thanks all!