They are not used anymore.

This way, we can remove it as a separate argument from
gtk_css_value_compute() and allow computation to only depend on one
thing: the style provider.

This is literally just renaming of the object (and the associated source
files). No other changes are in there.

We need to be able to compute different GtkCssImage values
depending on the scale, and we need this at compute time so that
we don't need to read any images other than the scale in used (to
e.g. calculate the image size). GtkStyleProviderPrivate is shared
for all style contexts, so its not right.

Here's the shortest description of the bug I can come up with:
When computing values, we have 3 kinds of dependencies:
(1) other properties ("currentColor" or em values)
(2) inherited properties ("inherit")
(3) generic things from the theme (@keyframes or @define-color)
Previously, we passed the GtkStyleContext as an argument, because it
provided these 3 things using:
(1) _gtk_style_context_peek_property()
(2) _gtk_style_context_peek_property(gtk_style_context_get_parent())
(3) context->priv->cascade

However, this makes it impossible to lookup values other than the ones
accessible via _gtk_style_context_peek_property(). And this is exactly
what we are doing in gtk_style_context_update_cache(). So when the cache
updates encountered case (1), they were looking up the values from the
wrong style data.

So this large patch essentially does nothing but replace the
context argument in all compute functions with new arguments for the 3
cases above:
(1) values
(2) parent_values
(3) provider

We apparently have a lot of computing code.

This is to allow animating arrays properly. I'm not really thrilled
about this solution (we leak propertys into the values again...), but
it's the best I can come up with - I prefer it to having N different
array types...

When values are computed, they might depend on various other values and
we need to track this so we can update the values when those other
values change. This is the first step in making that happen.

This patch does not do any dependency tracking at all, instead it uses
GTK_CSS_DEPENDS_ON_EVERYTHING as a sort of FIXME.

This is a reorganization of how value computing should be done.
Previously the GtkCssStyleProperty.compute vfunc was supposed to take
care of special cases when it needed those for computation. However,
this proved to be very complicated in cases where values were nested and
only the last value (of a common type) needed to be special cased.

A common example for this was the fallback handling for unresolvable
colors.

Now, we pass the property's ID along with all compute functions so we
can do the special casing where it's necessary.
Note that no actual changes happen in this commit. This will happen in
follow-ups.

This commit is essentially a large reorganization. Instead of all value
subtypes having their own compute function, there is the general
_gtk_css_value_compute() function that then calls a vfunc on the
subtype.