Currently, GtkCssProvider can emit ::parsing-error only during
the actual parsing, although the documentation hints that it might
happen at other times.
This commit adds a emit_error method to the GtkStyleProviderPrivate
interface that will let us emit errors from the compute() implementations
as well, which can be useful (e.g. if an image fails to load).
This gives a GtkSettings object for resolving system-dependant things -
like the default font family and font size.
No code does this yet, but we have an API.
Only GtkSettings implements this.
Make _gtk_style_provider_private_get_color() return a GtkCssValue (a
GtkCssColorValue to be exact) instead of GtkSymbolicColor.
With this, the symbolic color usage inside GTK is minimized.
We now use the GtkStleProviderPrivate interface, which hopefully is
faster and more conformant to CSS. Long term, it definitely should be
both.
I would have liked to split this up into multiple commits, but couldn't
find a way.
