This is mainly an attempt to merge the update_style() and validte()
vfuncs. Code is not there yet, but that's the idea.
Also, gtk_css_node_set_style() should not be public. And this gets
closer to that goal, too.
After measuring it, I realized the optimization never triggers for
Adwaita and rarely ever triggers for simple themes. So it is not
useful to keep it around.
This allows adding more API for it.
It also includes code that tracks modifications and invalidates siblings
and their positions whenever nodes get added or removed.
If we know the parent's get_path_for_child() implementation is safe to
be used with GtkCssNode because it doesn't do anything special, we do
that. Unfortunately that requires whitelisting vfuncs because the vfunc
is public API so anyone can override it.
Instead, use gtk_widget_get_path() which makes GtkWidget cache the path.
This is a temporary solution until we can get rid of widget paths.
This increases memory usage quite noticably.
The node declaration has the same functionality as
gtk_css_node_declaration_add_to_widget_path(). So instead of using that
function on a path, you can use the original path and the declaration in
a matcher.
So far the vfunc is kinda quirky (the path argument is an out argument
for something you have to free when you're done with the matcher), but
I'm about to change that.
We don't want to add the current classes to the widget path - which
might potentially be different after a gtk_style_context_save() - but
the root node's ones. So what better thing to do than actually using the
root node?
Instead of directly requesting the layout phase, register a tick
callback. This is what the docs suggest for animations and it's what we
need for the next commit.
... to a bunch of functions.
This requires a tiny change to the heuristics for the style cache - we
now cache styles when they have the same style provider as their parent
instead of when they have the default provider - but that change doesn't
have any effect in practice.
The parent refs the child, so gtk_css_node_set_parent() adds/removes a
reference.
We should probably refactor this so that we name the function
parent.add(node) instead of node.set_parent(parent) - makes the
refcounting more clear.
Instead of passing the style declaration, take the node's style
declaration. Add arguments to allow overriding the state for the one
case where this didn't work.
