bug#43397: 28.0.50; Adding tool bar items: update tool bar

[Caio Henrique]

Hi all,

I don't know if this is a bug or the expected behavior of the function
tool-bar-add-item-from-menu: 

1. emacs -Q
2. paste and eval this:
(progn
  (tool-bar-add-item-from-menu 'undo-redo
                               "redo" nil :vert-only t)
  (redraw-display)
  (force-mode-line-update))

I'm using both redraw-display and force-mode-line-update to try to force
the tool-bar to draw the icon (I know that I should'nt do this, I'm just
trying to figure if this is a bug); but the icon only appears when I
click one or two times with the mouse anywhere in the buffer. 

If there is a bug, this is possibly related to it:
https://lists.gnu.org/archive/html/emacs-devel/2020-09/msg00603.html
https://lists.gnu.org/archive/html/emacs-devel/2020-09/msg00726.html
https://lists.gnu.org/archive/html/emacs-devel/2020-09/msg00780.html

And also this:
https://lists.gnu.org/archive/html/emacs-devel/2020-09/msg01089.html
https://lists.gnu.org/archive/html/emacs-devel/2020-09/msg01101.html
> Eli: Here, the above displays nothing at all on the tool bar.
(If I click with the mouse anywhere in the buffer, that icon also gets
displayed for me) 

Thanks!

____
In GNU Emacs 28.0.50 (build 19, x86_64-pc-linux-gnu, GTK+ Version
3.24.13, cairo version 1.16.0)

Configured features:
XPM JPEG TIFF GIF PNG CAIRO SOUND DBUS GSETTINGS GLIB NOTIFY INOTIFY
LIBSELINUX GNUTLS LIBXML2 FREETYPE HARFBUZZ ZLIB TOOLKIT_SCROLL_BARS
GTK3 X11 XDBE XIM MODULES THREADS JSON PDUMPER