This introduces -DWLR_USE_UNSTABLE and adds information regarding the stability status to all headers. I started with a conservative set of headers to mark as stable: - types/wlr_matrix.h - util/edges.h - util/log.h - util/region.h - xcursor.h
The texture is managed by the surface's wlr_buffer now. In particular, the buffer can destroy the texture early if it becomes invalid.