fix(docs/helpful): add workarounds for recent Emacs 29.x issues

There's been a couple of recent changes in Emacs' master branch which
has affected the helpful package. These changes work around both issues,
and seems to let helpful keep working as before.

modules/documentation/siren-helpful.el

@@ -18,7 +18,21 @@
 
   :custom
   (helm-describe-function-function 'helpful-function)
-  (helm-describe-variable-function 'helpful-variable))
+  (helm-describe-variable-function 'helpful-variable)
+
+  :config
+  ;; TODO: Follow up on this workaround for the removal of the
+  ;; `read-symbol-positions-list' variable in Emacs 29.x. More details:
+  ;; https://github.com/Wilfred/elisp-refs/issues/35
+  (when (not (version< emacs-version "29.0"))
+    (defvar read-symbol-positions-list nil))
+
+  ;; TODO: Follow up this workaround required due to `help-fns--autoloaded-p'
+  ;; being changed to only accept a single argument in Emacs 29.x in commit:
+  ;; https://github.com/emacs-mirror/emacs/commit/1d1b664fbb9232aa40d8daa54a689cfd63d38aa9
+  (defun helpful--autoloaded-p (sym _buf)
+    "Return non-nil if function SYM is autoloaded."
+    (help-fns--autoloaded-p sym)))
 
 (provide 'siren-helpful)
 ;;; siren-helpful.el ends here