Don't include output rule disables if disabled by a plugin

[JoshuaKGoldberg]

For example, after #4, many generated ESLint configs will extend from eslint-plugin-prettier. There'll be no need to disable whitespace rules that are already disabled.

I believe this will require something like require-ing plugins to get rule settings from them...

[JoshuaKGoldberg]

I believe this was actually fixed by #78 as a subset of #13.