Add const to generated enum values() (#2011)

* Add const to generated enum values()

Enum values() functions return static arrays of static strings and could
be of compile time use. Make callable in const contexts.

* Add reference to PR in changelog next for const enum values()

* Correct changelog next target to all for const enum values()

Co-authored-by: Luca Palmieri <20745048+LukeMathWalker@users.noreply.github.com>