This should be an idempotent patch. The way to come up with this patch has been:

 * Run the first script attached to the bug and pipe it to xclip, then paste it
   in color.rs
 * Add the relevant #[derive] annotations and remove the color.mako.rs
   definition.
 * Reorder the values to match the ColorID definition, on which some widget
   prefs and caching stuff relies on.
 * Manually port some documentation from nsLookAndFeel.h
 * Run `rg 'eColorID_' | cut -d : -f 1 | sort | uniq >files`
 * Run the second script attached to the bug.
 * Manually fix usage of `LAST_COLOR` (adding the `End` variant), and adding
   casts to integer as needed.
 * Add an static assert so that people remember to update the prefs, rather than
   a comment on the definition :)

Differential Revision: https://phabricator.services.mozilla.com/D32610