core-lib: add auto-minor-mode, revise def-project-mode!

- Adds the auto-minor-mode package to replace our in-house
  implementation.
- Merges associate! into the def-project-mode! macro because associate!
  on its own is less useful than auto-minor-mode-alist,
  auto-minor-mode-magic-alist or hooks.
- Changes the semantics of :modes and :add-hooks properties of
  def-project-mode!. Its arguments are evaluated as is; lists will need
  to be quoted.

squash! core-lib: remove associate! macro

modules/lang/emacs-lisp/packages.el

@@ -11,3 +11,5 @@
 
 (when (featurep! :tools flycheck)
   (package! flycheck-cask))
+
+(package! buttercup)