bug#66765: 30.0.50; Building emacs with xinput2 breaks receiving XSendEvent events

[Ami Fischman <ami@fischman.org>]

1. Run: `emacs -Q` on an X11 display for a binary that's been built
with (the default) `--with-xinput2`
2. From another program, trigger an XSendEvent targeting the above
emacs' window sending a key event.
Expected:
3. The sent key event is seen by emacs.
Actual:
4. Emacs doesn't seem to receive the sent key event.

Simplest way to execute step 2 above is:
$ git clone http://github.com/epitron/xse.git
$ cd xse && ./configure  && xmkmf && make depend && make
$ xwininfo
(click the emacs window and note its reported "Window id" for the next command)
$ ./xse -win <EMACS_WINDOW_ID> -Debug '<Key>l'

When emacs is built with `--without-xinput2` the issue is gone, and
sent events are received properly.
Issue is not present in 27.1 or 28.1, but is present in 29.1 and HEAD.
Confirmed with a git bisect that the issue showed up when xinput2 was
enabled by default in
https://git.savannah.gnu.org/cgit/emacs.git/commit/?id=0105a4ddb8a58146f3fc71c265e57291c873af0b

I stumbled across this issue when upgrading from 27.1 to 29.1 and
noticing that ratpoison can no longer send its escape key (in my case,
this is C-a) to emacs, even though it has no problems sending the same
key to every other app on my system.

In GNU Emacs 30.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version
 3.24.33, cairo version 1.16.0) of 2023-10-25 built on <ELIDED>
Repository revision: 70e25298f160ffec62e363056904b6238a87d4e0
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12101004
System Description: Ubuntu 22.04.3 LTS

Configured using:
 'configure --prefix=<ELIDED> --enable-libsystemd
 --with-pop=yes
 --enable-locallisppath=/etc/emacs:/usr/local/share/emacs/29.1/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/29.1/site-lisp:/usr/share/emacs/site-lisp
 --with-sound=alsa --without-gconf --with-mailutils --with-cairo
 --with-x=yes --with-x-toolkit=gtk3 --with-toolkit-scroll-bars
 --with-imagemagick --with-json --with-tree-sitter --with-xwidgets
 'CFLAGS=-g -O2 -fstack-protector-strong -w' 'CPPFLAGS=-Wdate-time
 -D_FORTIFY_SOURCE=2' 'LDFLAGS=-Wl,-Bsymbolic-functions -Wl,-z,relro''

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ
IMAGEMAGICK JPEG JSON LCMS2 LIBOTF LIBSELINUX LIBSYSTEMD LIBXML2
M17N_FLT MODULES NOTIFY INOTIFY PDUMPER PNG RSVG SECCOMP SOUND SQLITE3
THREADS TIFF TOOLKIT_SCROLL_BARS TREE_SITTER X11 XDBE XIM XINPUT2 XPM
XWIDGETS GTK3 ZLIB

Important settings:
  value of $LC_ALL:
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  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
  minibuffer-regexp-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
cl-loaddefs cl-lib sendmail rfc2047 rfc2045 ietf-drums mm-util
mail-prsvr mail-utils rmc iso-transl tooltip cconv eldoc paren electric
uniquify ediff-hook vc-hooks lisp-float-type elisp-mode mwheel
term/x-win x-win term/common-win x-dnd touch-screen 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 xwidget-internal dbusbind
inotify lcms2 dynamic-setting system-font-setting font-render-setting
cairo gtk x-toolkit xinput2 x multi-tty move-toolbar
make-network-process emacs)

Memory information:
((conses 16 37691 9512) (symbols 48 5216 0) (strings 32 13286 1532)
 (string-bytes 1 375218) (vectors 16 10300)
 (vector-slots 8 156562 17668) (floats 8 38 21) (intervals 56 259 0)
 (buffers 992 10))