Use core's starterkit for subtheming

So with this MR I am able to create a subtheme using the native Starterkit theme generation doing this:

# placed in radix theme directory
cp -r src/kits/radix_starterkit ../
# and then running from drupal webroot
php  core/scripts/drupal generate-theme --starterkit radix_starterkit  mytheme

Some logic is applied from the native generator, and some other (includes replacements, some info.yml replacements, and schema replacements)
are added in new https://git.drupalcode.org/issue/radix-3365825/-/blob/5.0.x/src/kits/rad... .

PS: variable-dark is also added to subtheme _init.scss (it was accidentally merged also) as said in: https://stackoverflow.com/questions/75873195/getting-primary-primary-tex...

Okay this is amazing work Aleix, I had this on my todo list with low priority but I believe you've done the job 👏
I'll review and play around and see if I can start a new 5.1.x along with some other changes for this

Great work

For now merged it into 5.1.x dev branch, needs more work I believe and a bit of restructuring, I assume copy/pasting the starterkit into themes directory is not the best approach, we either have to redo the Radix itself or directly point to the starterkit path

Giving direct path of radix_starterkit fails, need to investigate it a bit more

It's something complex, I guess, as it comes from how extensiondisovery scans: https://api.drupal.org/api/drupal/core%21lib%21Drupal%21Core%21Extension...

I filled a feature request in https://www.drupal.org/project/drupal/issues/3367079 ✨ Core theme generator cannot be used because is not finding theme's included subtheme Active ...

Thanks for the help here Aleix

Well that was blazingly FAST, thank you @aleix

In commons we trust :)

As of now in 5.1.x we can leverage the current drush command to create the subtheme with core starterkit, closing this for now.
We can for sure improve it at a later stage if needed

Automatically closed - issue fixed for 2 weeks with no activity.