Api touchups
Two (or three) changes:
- Make GtkNativeInterface private, since we are not convinced that there should be out-of-tree implementations
- Make gtk_native_get_for_surface return GtkNative
- Drop all the defines for style classes - half of them are outdated or unsupported, none of them are meaningfully documented. We document the literal strings for supported style classes on widgets
Edited by Matthias Clasen