The new CSS border-spacing does what Grid::(row|column)_spacing and
Box::spacing already did, i.e. controlling the space added between child
widgets, so it’s not a replacement for Container::border-width.
Now that priv->area is guaranteed to be constructed by us, and not
passed in by a user, we can move it to the .ui file and stop manually
managing its lifetime altogether. And once the area is there, we can
move the menu there too (and stop pointlessly destroying/rebuilding it).
We already have cell_layout_is_sensitive() to get whether at least one
cell in a Layout is sensitive, which we need because CellLayout/View
do not implement foreach(). So, since we wrote that, we can use it to
check our CellArea too, instead of doing foreach with a custom callback.
It was looping over all items, not breaking out when it found the first
selectable one, and then selecting the _last_ selectable one (if any)
found. So, it did exactly the opposite of its name. This made me quite
baffled when opening a submenu with right-arrow put me at its last item.
Originally, the loop set to_select and broke if the current item was
selectable and not tear-off, meaning that it would correctly select the
first suitable item. However, when tear-off functionality was removed
in commit 4ed9452e90, so was the break.
combo_box_popdown() currently skips popping down our menu if it is NULL.
But the required call to this at end-of-life was in destroy(), by which
point dispose() already NULLed the menu, so Menu::popdown() would never
run, even if it should. Fix this by trying popdown() earlier in unmap().
Also, add a converse assurance that we don’t popup() while not mapped.
Even once we remove all the now-pointless NULL checks, destroy() was the
wrong place to call combo_box_popdown(), and unmap() is the right place.
gtk_init() removed its support for supporting arguments, so we ought to do
likewise for Windows, which actually defines items that call gtk_init()
the old way (and also get rid of argument support in those functions,
since the direction is to not support them).
https://bugzilla.gnome.org/show_bug.cgi?id=773299
