[12.x] [meta] Deprecate dependencies, libraries, modules, and themes that will be removed from Drupal 12 core

Amending attribution.

The very latest we can deprecate these modules is in the same minor release that comes out when 12.0.0 is released, but there are multiple steps involved before actual deprecation so it's really time to get this moving now.

I added a stub CTA about this in our post draft at the end:

Help us get ready for Drupal 12!

Core modules are actually not disruptive to deprecate, because we can create an equivalent package in contrib and provide sites a smooth upgrade path for these modules from Drupal 11 core to Drupal 12 contrib. Take a look at the list of modules and other dependencies planned for removal from Drupal 12 🌱 [12.x] [meta] Deprecate dependencies, libraries, modules, and themes that will be removed from Drupal 12 core Active , and consider helping move these issues forward.