scanner: emit event wrapper functions for server

Generate typed wrapper functions for sending events in a server.

This allows compile time type checking, unlike the existing method of
calling the variadic function wl_resource_post_event().

The stuff in wayland-server.h had to be slightly reordered to have all
(forward) declarations before use.

Signed-off-by: Pekka Paalanen <ppaalanen@gmail.com>