bug#70515: 30.0.50; which-function-mode error in lua-ts-mode

[john muhl <jm@pub.pink>]

  -- test.lua
  local function f(x)
      print(x)
  end

  emacs -Q test.lua
  M-x which-function-mode

  Error running timer ‘which-func-update’:
  (error "Error in which-func-update:
  (invalid-function #<treesit-node function_declaration in 1-37>)")

Patch to follow.

In GNU Emacs 30.0.50 (build 1, x86_64-pc-linux-gnu) of 2024-04-21 built
 on localhost
Repository revision: 4773ecb93193495f141e5d60c0c5ded58eaa2c98
Repository branch: master
System Description: Fedora Linux 39 (Thirty Nine)

Configured using:
 'configure --without-x --without-native-compilation'

Configured features:
ACL DBUS GMP GNUTLS GPM LIBSELINUX LIBSYSTEMD LIBXML2 MODULES NOTIFY
INOTIFY PDUMPER SECCOMP SOUND SQLITE3 THREADS TREE_SITTER XIM ZLIB

Important settings:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Lua

Minor modes in effect:
  which-function-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  show-paren-mode: t
  electric-indent-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  minibuffer-regexp-mode: t
  line-number-mode: t
  transient-mark-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message mailcap yank-media puny dired
dnd dired-loaddefs rfc822 mml mml-sec password-cache epa derived epg
rfc6068 epg-config gnus-util text-property-search time-date subr-x
mm-decode mm-bodies mm-encode mail-parse rfc2231 mailabbrev gmm-utils
mailheader sendmail rfc2047 rfc2045 ietf-drums mm-util mail-prsvr
mail-utils cus-start cus-load which-func imenu cl-seq lua-ts-mode
treesit cl-loaddefs cl-lib comint regexp-opt ansi-osc ansi-color ring
term/xterm xterm byte-opt gv bytecomp byte-compile rmc iso-transl
tooltip cconv eldoc paren electric uniquify ediff-hook vc-hooks
lisp-float-type elisp-mode tabulated-list replace newcomment text-mode
lisp-mode prog-mode register page tab-bar menu-bar rfn-eshadow isearch
easymenu timer select mouse jit-lock font-lock syntax font-core
term/tty-colors frame minibuffer nadvice seq simple cl-generic
indonesian philippine cham georgian utf-8-lang misc-lang vietnamese
tibetan thai tai-viet lao korean japanese eucjp-ms cp51932 hebrew greek
romanian slovak czech european ethiopic indian cyrillic chinese
composite emoji-zwj charscript charprop case-table epa-hook
jka-cmpr-hook help abbrev obarray oclosure cl-preloaded button loaddefs
theme-loaddefs faces cus-face macroexp files window text-properties
overlay sha1 md5 base64 format env code-pages mule custom widget keymap
hashtable-print-readable backquote threads dbusbind inotify multi-tty
make-network-process emacs)

Memory information:
((conses 16 66424 9105) (symbols 48 7625 0) (strings 32 18124 1778)
 (string-bytes 1 437334) (vectors 16 8799) (vector-slots 8 77160 4863)
 (floats 8 28 1) (intervals 56 253 2) (buffers 992 11))