Previously, we haven't added this because there were plans to use these
declarations at a higher abstraction level where one declaration potentially
contains more than one socket. This hasn't happened yet, and we are also using
other ways to achieve dynamic socket amounts (using dynamic declarations).
Therefore, it is reasonable to simplify the code by storing the integer socket
type in the declaration directly.
Pull Request: https://projects.blender.org/blender/blender/pulls/119691
25a10c211f