New :completion corfu module

Development modules
#21

Should we style this together and set defaults in the Doom module? Corfus own defaults are kind of underwhelming if you compare it to company.

Maybe set the styling according to the theme even? Like this:

  (custom-set-faces!
    `(corfu-current
      :background ,(doom-blend (doom-color 'blue) (doom-color 'bg-alt) 0.3)
      :extend t)))
#22

I’m experimenting with :completion corfu and I think that there are two keybindings missing. In insert state C-x C-f is bound to find-file, whereas in vim and :completion company it allow to complet the file’s name. So I think C-x C-f should be bound to cape-file in insert state. For same reason C-x C-o should be bound to corfu-next in insert state.

otherwise thank for work on this module !