The "paint" signal of ClutterActor is deprecated and will be removed. We
have a good replacement to get notified about stage paints nowadays,
that is "after-paint" on ClutterStage, so switch to that signal where it
makes sense.
I didn't bother to update the few tests (namely Clutters
conform/texture-fbo.c, conform/text-cache.c,
interactive/test-cogl-multitexture.c and Cogls
conform/test-multitexture.c, conform/test-texture-mipmaps.c) where it's
harder to replace the signal since we don't build those anyway.
https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1522