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/emacs/vc/config.el

@@ -10,7 +10,7 @@
 
 (after! git-timemachine
   ;; HACK Waiting for https://gitlab.com/pidu/git-timemachine/issues/77
-  (def-advice! +vc-git-timemachine-show-commit-a ()
+  (defadvice! +vc--git-timemachine-show-commit-a ()
     "Fix `git-timemachine-show-commit'."
     :override #'git-timemachine-show-commit
     (interactive)