Add "Neurodivergent" to demographic information options on user accounts

Problem/Motivation

The demographic information field on drupal.org user accounts does not list "Neurodivergent" as an option. Can we add it to this list? Being autistic myself, I don't identify with any of the existing options.

Proposed resolution

All of the examples for "Learning Differences" are considered neurodivergent. So a simple solution is to just relabel "Learning Differences" to "Neurodivergent".

Remaining tasks

1. Update the text on the Demographic information → page
2. Update the label in the form itself
3. (Optionally) Update the key also, but that's probably overkill (requiring a hook_update(), etc.)

User interface changes

N/A (except for the label change described above)

API changes

N/A

Data model changes

N/A (unless we decide to do #3 above)