The function does not exist.

That function does not make sense at all in a CSS world. So better don't
support it anymore.

As part of removing all the cairo_surace_t usage. There's still
gtk_render_icon for the same purpose that takes a GdkTexture*

Remove all the old 2.x and 3.x version annotations.
GTK+ 4 is a new start, and from the perspective of a
GTK+ 4 developer all these APIs have been around since
the beginning.

This gets rid of more GdkPixbuf in the API.

Update all callers.

This is long-gone drawing API.

Move the icon size lookup API into gtkicontheme.c

The new function, gtk_render_background_get_clip answers the
question: what pixels are affected if I call gtk_render_background ?

The long-term goal is to have APIs that answer this question for
all rendering primitives.