cmake: build type propagation release notes

[joukewitteveen]

This is a follow up to #12947. It contains the release note snippet as well as the formatting/typing changes requested by @dcbaker. I considered adding annotations and all-caps for the constants in cmake/common.py as well, but since the language_map variable from that module is 'exported' and used elsewhere I decided not to. It may make sense to at least add typing information to that variable, because I wasn't sure whether it was final (i.e. read-only), or whether it would be okay for some other code to extend it.

~Many of the constants typed as sequences could have been typed as collections because that more closely reflects how they are used. However, there are no distinct types for immutable and mutable collections and I figured the immutable nature was more important than the smaller 'interface' of a collection.~ edit: of course a Collection is immutable: it doesn't have __setitem__! :facepalm:

[dcbaker]

Thanks for following up on this!

[eli-schwartz]

Unsure why this is in a milestone since:

• annotations aren't a backportable bugfix
• release notes don't make sense to backport, if the release notes are lacking for a previous release, we would have to edit them in place
  • the feature it is a release note for, is not on the milestone