bug#59628: 29.0.50; treesit-beginning/end-of-defun problems in C/C++

[Eli Zaretskii <eliz@gnu.org>]

To reproduce, visit any C source file in the Emacs tree, turn on c-ts-mode
or c++-ts-mode, go to the middle of some function, and type

   M-: (treesit-beginning-of-defun) RET
or
   M-: (treesit-end-of-defun) RET

This will move point to very strange places, which generally are neither the
beginning nor the end of the function.  In very simple functions, like this
one:

  void
  __executable_start (void)
  {
    emacs_abort ();
  }

the result is correct.  But once the function is even slightly more
complicated, for example, like this:

  static int
  margin_glyphs_to_reserve (struct window *w, int total_glyphs, int margin)
  {
    if (margin > 0)
      {
	int width = w->total_cols;
	double d = max (0, margin);
	d = min (width / 2 - 1, d);
	/* Since MARGIN is positive, we cannot possibly have less than
	   one glyph for the marginal area.  */
	return max (1, (int) ((double) total_glyphs / width * d));
      }
    return 0;
  }

the results are very far off the mark.

These two functions are the only ones to move by defuns in treesit-based
modes, right?  So they should be improved, IMO.

In GNU Emacs 29.0.50 (build 2273, i686-pc-mingw32) of 2022-11-27 built
 on HOME-C4E4A596F7
Repository revision: 80dcd78ff1fce3241043edf1951289eef0bf50c9
Repository branch: master
Windowing system distributor 'Microsoft Corp.', version 5.1.2600
System Description: Microsoft Windows XP Service Pack 3 (v5.1.0.2600)

Configured using:
 'configure -C --prefix=/d/usr --with-wide-int
 --enable-checking=yes,glyphs 'CFLAGS=-O0 -gdwarf-4 -g3''

Configured features:
ACL GIF GMP GNUTLS HARFBUZZ JPEG JSON LCMS2 LIBXML2 MODULES NOTIFY
W32NOTIFY PDUMPER PNG RSVG SOUND SQLITE3 THREADS TIFF
TOOLKIT_SCROLL_BARS TREE_SITTER WEBP XPM ZLIB

Important settings:
  value of $LANG: ENU
  locale-coding-system: cp1255

Major mode: C

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  show-paren-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  line-number-mode: t
  indent-tabs-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
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
misearch multi-isearch vc-git diff-mode easy-mmode vc-dispatcher
c-ts-mode rx treesit cl-seq cl-loaddefs cl-lib rmc iso-transl tooltip
cconv eldoc paren electric uniquify ediff-hook vc-hooks lisp-float-type
elisp-mode mwheel dos-w32 ls-lisp disp-table term/w32-win w32-win
w32-vars term/common-win tool-bar dnd fontset image regexp-opt fringe
tabulated-list replace newcomment text-mode lisp-mode prog-mode register
page tab-bar menu-bar rfn-eshadow isearch easymenu timer select
scroll-bar 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 w32notify w32 lcms2 multi-tty make-network-process emacs)

Memory information:
((conses 16 60472 7440)
 (symbols 48 7296 0)
 (strings 16 20076 2163)
 (string-bytes 1 498360)
 (vectors 16 11107)
 (vector-slots 8 164960 11733)
 (floats 8 29 319)
 (intervals 40 2962 92)
 (buffers 896 14))