bug#81662: 31.1; [FR] Registers pointing to bookmarks

I propose to support bookmarks as register content. This way register
keys can be used as quick access keys to bookmarks. Bookmarks are
supported by many major modes. The feature can be implemented easily
since register.el uses generic methods:

(cl-defmethod register-val-describe ((bm (head bookmark)) _verbose)
  (princ (format "Bookmark \"%s\"" (cdr bm))))

(cl-defmethod register-val-jump-to ((bm (head bookmark)) _delete)
  (bookmark-maybe-load-default-file)
  (bookmark-jump (cdr bm)))

Furthermore a command bookmark-to-register could be added. Does this
look like a good addition or are there better alternatives? Thanks!

In GNU Emacs 31.1 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.49,
 cairo version 1.18.4) of 2026-08-17
Windowing system distributor 'The X.Org Foundation', version 11.0.12101016
System Description: Debian GNU/Linux 13 (trixie)

Configured using:
 'configure --prefix=$HOME/.local/share/emacs-install
 --without-compress-install --with-tree-sitter=ifavailable
 --with-native-compilation --with-dbus --without-selinux
 --without-threads --disable-gc-mark-trace --without-gsettings
 --without-gpm --with-cairo --with-cairo-xcb --with-xinput2
 --with-x-toolkit=gtk3 --without-toolkit-scroll-bars 'CFLAGS=-O3
 -mtune=native -march=native''

Configured features:
CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS HARFBUZZ JPEG LIBOTF LIBSYSTEMD
LIBXML2 MODULES NATIVE_COMP NOTIFY INOTIFY PDUMPER PNG RSVG SECCOMP
SOUND SQLITE3 TIFF TREE_SITTER WEBP X11 XCOMPOSITE XDBE XFIXES XIM
XINERAMA XINPUT2 XPM XRANDR XRENDER XSHAPE XSYNC GTK3 ZLIB