It was always looking at the 'color' keyword for the parent context
instead of only doing that when used with the 'color' property.
Tested by border-color-default.ui reftest.
This reverts commit c276f53796 and
implements the same feature using the compute function.
A nice side effect is that gtk_style_property_get_border() and
gtk_style_property_get("border") to the same thing now.
We want to make sure to fall back to the initial value of the property
if resolving fails.
This is kinda tricky, because the initial value itself might need
resolving, too.
This would make the internal properties custom properties. And they are
not.
Also get rid of default initial values, we now specify the correct one
at all times.
