refactor(corfu): settings and keybinding overhaul

Previously, a distinction was made only between "regular" style (assumed
to be for people who prefer to cycle directionally and commit with RET)
and +tng (assumed to be for people who prefer TAB and auto-commit). This
made composing further variations harder on the user, as they would have
to work around our bindings. Now we provide a flag per feature, and the
user can compose to their liking. Some variable options were turned into
flags and the global CAPF list was pruned, suggesting to use individual
keys for those functions if required.

modules/completion/corfu/autoload.el

@@ -1,13 +1,5 @@
 ;;; completion/corfu/autoload.el -*- lexical-binding: t; -*-
 
-;;;###autoload
-(defun +corfu-complete-and-exit-minibuffer ()
-  (interactive)
-  (if (>= corfu--index 0)
-      (corfu-complete)
-    (corfu-insert))
-  (exit-minibuffer))
-
 ;;;###autoload
 (defun +corfu-move-to-minibuffer ()
   "Move the current list of candidates to your choice of minibuffer completion UI."