def-advice!->defadvice! & conform to new advice conventions

This commit does two things:

- Renames def-advice! to defadvice!, in the spirit of naming convenience
  macros after the function/macro they enhance or replace.
- Correct the names of advice functions to indicate visibility and
  intent. A public advice function like doom-set-jump-a is meant to be
  used elsewhere. A private one like +dired--cleanup-header-line-a
  shouldn't -- it likely won't work anywhere but the function(s) it was
  made to advise.

modules/editor/fold/config.el

@@ -28,7 +28,7 @@
         ;; Nicer code-folding overlays (with fringe indicators)
         hs-set-up-overlay #'+fold-hideshow-set-up-overlay-fn)
 
-  (def-advice! +fold-hideshow-ensure-mode-a (&rest _)
+  (defadvice! +fold--hideshow-ensure-mode-a (&rest _)
     "Ensure `hs-minor-mode' is enabled."
     :before '(hs-toggle-hiding hs-hide-block hs-hide-level hs-show-all hs-hide-all)
     (unless (bound-and-true-p hs-minor-mode)