lang/emacs-lisp: replace xref with elisp-def

Possibly better goto-definition behavior than xref; needs more testing.

modules/lang/emacs-lisp/config.el

@@ -31,7 +31,9 @@
 (after! elisp-mode
   (set-repl-handler! 'emacs-lisp-mode #'+emacs-lisp/repl)
   (set-eval-handler! 'emacs-lisp-mode #'+emacs-lisp-eval)
-  (set-lookup-handlers! 'emacs-lisp-mode :documentation 'info-lookup-symbol)
+  (set-lookup-handlers! 'emacs-lisp-mode
+    :definition    #'elisp-def
+    :documentation #'info-lookup-symbol)
   (set-docset! 'emacs-lisp-mode "Emacs Lisp")
   (set-pretty-symbols! 'emacs-lisp-mode :lambda "lambda")
   (set-rotate-patterns! 'emacs-lisp-mode

modules/lang/emacs-lisp/packages.el

@@ -5,6 +5,7 @@
 (package! highlight-quoted)
 (package! macrostep)
 (package! overseer)
+(package! elisp-def)
 
 (when (featurep! :feature syntax-checker)
   (package! flycheck-cask))