💥 Rename def-package! -> use-package!

Calling this pivotal macro "def-package!" has frequently been a source
of confusion. It is a thin wrapper around use-package, and it should be
obvious that it is so. For this reason, and to match the naming
convention used with other convenience macros/wrappers, it is now
use-package!.

Also changes def-package-hook! -> use-package-hook!

The old macros are now marked obsolete and will be removed when straight
integration is merged.

core/autoload/help.el

@@ -381,7 +381,7 @@ current file is in, or d) the module associated with the current major mode (see
     (split-string
      (shell-command-to-string
       (format "git grep --no-break --no-heading --line-number '%s %s\\($\\| \\)'"
-              "\\(^;;;###package\\|(after!\\|(def-package!\\)"
+              "\\(^;;;###package\\|(after!\\|(use-package!\\)"
               package))
      "\n" t)))