Add +prescient option for :completion ivy

This provides an alternative backend for filtering and sorting ivy
searches. Uses prescient instead of flx for fuzzy completion when both
+prescient and +fuzzy are selected.

modules/completion/company/config.el

@@ -47,6 +47,7 @@
 (def-package! company-prescient
   :hook (company-mode . company-prescient-mode)
   :config
+  ;; NOTE prescient config duplicated with `ivy'
   (setq prescient-save-file (concat doom-cache-dir "prescient-save.el"))
   (prescient-persist-mode +1))