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

[Robert Pluim]

>>>>> On Thu, 17 Sep 2020 16:45:16 +0300, Eli Zaretskii <eliz@gnu.org> said:

    >> The GTK code just adds items to the toolbar in order. Itʼs possible in
    >> GTK to specify negative positions for toolbar items, but that just
    >> means 'append', not 'align to right border' as far as I can see.

    Eli> Thanks.

    Eli> If we cannot control the placement of icons on GTK, then I guess it
    Eli> makes little sense to add features to do this in our native tool bar,
    Eli> since most users will be unable to take advantage of it.

Actually we *can* control the placement of the icons on the GTK
toolbar, as it turns out. Buried in the fine print is this sentence:

    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.

The other way to do this would be to add toolbar items at specific
positions in the toolbar, but I couldn't find an api that answered the
question "how many items of size x can I add before I reach the right
border of the window" (and then weʼd have to recalculate the positions
if the frame changes size).

Robert