egl/gallium/kopper: hook up zsbuf invalidation (for real this time I'm serious)

!21317 (merged) attempted to hook up ancillary buffer invalidation, and it succeeded.

unfortunately, this doesn't actually help zink do anything because the invalidate is triggered so late that it's entirely impossible to merge it onto any renderpass

instead, since the zsbuf can always be invalidated in this scenario, try a different approach and just set a property directly on the framebuffer state to let the driver pick it up at the start of the renderpass

other frontends should be able to implement pretty easily if desired, but for now only kopper implements it (zink changes have dependencies)