💥 Replace core-popup with new feature/popup module

This is a breaking change! Update your :popup settings. Old ones will
throw errors!

Doom's new popup management system casts off its shackles (hur hur) and
replaces them with the monster that is `display-buffer-alist`, and
window parameters.

However, this is highly experimental! Expect edge cases.  Particularly
with org-mode and magit (or anything that does its own window
management).

Relevant to #261, #263, #325

modules/completion/helm/config.el

@@ -42,7 +42,6 @@
   (after! helm-mode
     (add-to-list 'helm-completing-read-handlers-alist '(find-file-at-point . nil)))
 
-  (set! :popup "\\` ?\\*[hH]elm.*?\\*\\'" :size 14 :regexp t)
   (setq projectile-completion-system 'helm)
 
   ;;; Helm hacks