bug#43405: Tool bar item doesn't align to the right edge

[Robert Pluim]

>>>>> On Thu, 17 Sep 2020 17:54:15 +0300, Eli Zaretskii <eliz@gnu.org> said:

    >> From: Robert Pluim <rpluim@gmail.com>
    >> Cc: 43405@debbugs.gnu.org,  juri@linkov.net
    >> Date: Thu, 17 Sep 2020 16:43:37 +0200
    >> 
    >> If the GtkToolbar child property "expand" is TRUE and the property
    >> "draw" is set to FALSE, the effect is to force all following items to
    >> the end of the toolbar.
    >> 
    >> So if you do the following, all toolbar items added after this
    >> separator end up on the right:
    >> 
    >> ti = gtk_separator_tool_item_new ();
    >> gtk_tool_item_set_expand (ti, true);
    >> gtk_separator_tool_item_set_draw (GTK_SEPARATOR_TOOL_ITEM (ti), true);
    >> gtk_toolbar_insert (GTK_TOOLBAR (wtoolbar), ti, j);
    >> 
    >> It does produce an ugly empty patch in the middle of the toolbar
    >> thatʼs a different colour though.

    Eli> So you are saying that, while possible, doing this is not really
    Eli> workable, since it produces ugly display?

You know this is 2020, so truth == lies, and lies == truth, right?
So, once I actually follow the documentation and pass 'false' in the right
place, the toolbar looks correct :-)

Now the question is: do we want to expose this to lisp, and if so,
how? I mean, I have no idea if the macOS or MS-Windows tool bar have
a similar feature.

Robert