wayland: fix warnings with more recent protocol version

Fixes a missing initializer warning for axis_value120. We currently enforce version = 5 for the wl_seat version, and it's available starting with wl_pointer version 8, which means that we don't need to set a function handler for now.

Fixes a missing initializer warning for wm_capabilities. It's available starting with xdg-toplevel version 5, and we use xdg-wm-base version 1 or the version adding configure_bounds which is version 4, so we don't need to set a handler for now.