next: Fix #74258

Next had a few issues with its packaging:
* the platform port was exposed in all-packages
  And this is not useful for outside users.
  It's now a local attribute in the next package.

* the platform port wasn't wrapped correctly
  It appears that the lisp core was being wrapped,
  when instead the actual gtk application that's
  called within the lisp core had to be wrapped.

* codestyle/indentation