bug#51267: 29.0.50; 'special-mode-map' keys missing from 'diff-mode-shared-map'

[bandali]

After recent changes in diff-mode, keys defined in 'special-mode-map'
seem to be missing from 'diff-mode-shared-map'.  This can be seen e.g.
in *vc-diff* buffers, where keys like "q" and "g" don't work anymore.

In GNU Emacs 29.0.50 (build 2, x86_64-pc-linux-gnu, X toolkit, cairo version 
1.16.0, Xaw3d scroll bars)
 of 2021-10-18 built on langa
Repository revision: 7d12c06725d733f1ea223f5fe55d506c71e44370
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12011000
System Description: Trisquel GNU/Linux Nabia (10.0)

Configured using:
 'configure --without-gconf --without-gsettings --without-gpm
 --with-x-toolkit=lucid --with-xaw3d --with-mailutils'

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS HARFBUZZ JPEG JSON LCMS2
LIBOTF LIBSELINUX LIBSYSTEMD LIBXML2 M17N_FLT MODULES NOTIFY INOTIFY
PDUMPER PNG RSVG SECCOMP SOUND THREADS TIFF TOOLKIT_SCROLL_BARS X11
XAW3D XDBE XIM XPM LUCID ZLIB

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

Major mode: Group

Minor modes in effect:
  gnus-topic-mode: t
  gnus-undo-mode: t
  yas-global-mode: t
  yas-minor-mode: t
  server-mode: t
  global-hl-todo-mode: t
  pixel-scroll-mode: t
  display-battery-mode: t
  recentf-mode: t
  display-time-mode: t
  save-place-mode: t
  savehist-mode: t
  winner-mode: t
  global-auto-revert-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  show-paren-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  global-prettify-symbols-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  temp-buffer-resize-mode: t
  buffer-read-only: t
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow sort gnus-cite flyspell ispell mail-extr emacsbug sendmail
gnus-topic nndraft nnmh utf-7 rfc2104 network-stream nsm nnfolder nnnil
gnus-agent gnus-srvr gnus-score score-mode nnvirtual gnus-msg gnus-art
mm-uu mml2015 mm-view mml-smime smime dig nntp gnus-cache gnus-sum shr
kinsoku svg dom gnus-group gnus-undo gnus-start gnus-dbus gnus-cloud
nnimap nnmail mail-source utf7 netrc nnoo parse-time iso8601 gnus-spec
gnus-int gnus-range message rmc puny dired-x dired dired-loaddefs rfc822
mml mml-sec epa derived epg rfc6068 epg-config mm-decode mm-bodies
mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader gnus-win
gnus nnheader gnus-util rmail rmail-loaddefs rfc2047 rfc2045 ietf-drums
text-property-search time-date mail-utils mm-util mail-prsvr boxquote
rect cl-extra yasnippet help-mode server hl-todo pcase easy-mmode
delight format-spec pixel-scroll battery dbus recentf tree-widget
wid-edit time xml finder-inf info package browse-url url url-proxy
url-privacy url-expand url-methods url-history url-cookie url-domsuf
url-util mailcap url-handlers url-parse auth-source cl-seq eieio
eieio-core eieio-loaddefs password-cache json map url-vars seq subr-x
byte-opt bytecomp byte-compile cconv bandali-po saveplace savehist
bandali-erc bandali-message bandali-gnus bandali-dired bandali-ibuffer
ibuf-macs bandali-eshell bandali-org advice winner ring autorevert
filenotify cl-macs gv cl-loaddefs cl-lib iso-transl tooltip eldoc paren
electric uniquify ediff-hook vc-hooks lisp-float-type elisp-mode mwheel
term/x-win x-win term/common-win x-dnd 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 cl-generic 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 simple abbrev obarray cl-preloaded nadvice
button loaddefs faces cus-face macroexp files window text-properties
overlay sha1 md5 base64 format env code-pages mule custom widget
hashtable-print-readable backquote threads dbusbind inotify lcms2
dynamic-setting font-render-setting cairo x-toolkit x multi-tty
make-network-process emacs)

Memory information:
((conses 16 186788 23177)
 (symbols 48 17908 7)
 (strings 32 59330 2484)
 (string-bytes 1 1877073)
 (vectors 16 32154)
 (vector-slots 8 383305 15316)
 (floats 8 216 81)
 (intervals 56 694 48)
 (buffers 992 21))