bug#69463: 29.2; Isearch help icon has inconsistent size

[Juri Linkov <juri@linkov.net>]

> When you press CTRL+s, I-search is activated, that provides a custom
> toolbar with dedicated icons and lets one enter what to search in the
> mode line.
>
> Unfortunately, in the toolbar there is a help icon, shaped as a life
> buoy, that is too big or at least inconsistently big wrt the other icons.
> As a consequence, when I-search is activated the emacs windows
> becomes bigger to accomodate space for the taller toolbar.
>
> Not only having the window changing its size causes some inconvenience
> because the text you are trying to focus on moves up and down. There is
> a major problem if the emacs window is already vertically maximized
> before you start searching. In fact, in this case there is no space for
> the window to grow. As a consequence, the mode line goes out of the
> screen and you cannot use it to search!

This behavior is system-dependent.  For example,
I can't reproduce it on these configurations:

GNU Emacs 29.1.90 (build 1, x86_64-pc-linux-gnu,
cairo version 1.16.0)

GNU Emacs 30.0.50 (build 1, x86_64-pc-linux-gnu, X toolkit,
cairo version 1.16.0, Xaw3d scroll bars)

GNU Emacs 30.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.20,
cairo version 1.16.0)

Strange, the last is similar to your configuration:

> In GNU Emacs 29.2 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.40,
> cairo version 1.18.0)