fix(tazjin/emacs): fix completion related problems

A while ago I decided to experiment with corfu and orderless instead of
company/prescient. This was prompted by issues which I had in EXWM, where some
sort of UI race with company elements could lock up a whole frame.

Now that I'm not on EXWM anymore this doesn't really matter, so I can bring back
company and set up prescient again correctly, fixing a whole bunch of issues
along the way:

* Completion issues where not all matching candidates where shown based on
  cursor position (I honestly have no idea what caused this and what was going
  on there, never figured it out, but enabling prescient properly fixes it).

* Code completion works again. Corfu, as I understand it, is technically
  better/cleaner/whatever than company - but it doesn't work anywhere,
  especially not in telega.el where I need completion more than anywhere else.

With this commit my Emacs behaves a lot better again.

Change-Id: I8f082de8211dd3be3bb7a0663d43d414cc320e49
Reviewed-on: https://cl.tvl.fyi/c/depot/+/12690
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>
Autosubmit: tazjin <tazjin@tvl.su>

users/tazjin/emacs/config/init.el

@@ -29,6 +29,10 @@
 
 (use-package browse-kill-ring)
 
+(use-package company
+  :config
+  (global-company-mode))
+
 (use-package consult
   :bind
   ("C-c r g" . consult-ripgrep)
@@ -68,6 +72,14 @@
   (prescient-persist-mode)
   (setq completion-styles '(basic prescient)))
 
+(use-package vertico-prescient
+  :config
+  (vertico-prescient-mode))
+
+(use-package company-prescient
+  :config
+  (company-prescient-mode))
+
 (use-package rainbow-delimiters :hook (prog-mode . rainbow-delimiters-mode))
 (use-package rainbow-mode)
 (use-package s)