server: Make wl_object and wl_resource opaque structs

With the work to add wl_resource accessors and port weston to use them,
we're ready to make wl_resource and wl_object opaque structs.  We keep
wl_buffer in the header for EGL stacks to use, but don't expose it by
default.  In time we'll remove it completely, but for now it provides a
transition paths for code that still uses wl_buffer.

Reviewed-by: Jason Ekstrand<jason@jlekstrand.net>

tests/client-test.c

@@ -31,8 +31,8 @@
 #include <sys/types.h>
 #include <sys/stat.h>
 
-#include "wayland-server.h"
 #include "wayland-private.h"
+#include "wayland-server.h"
 #include "test-runner.h"
 
 struct client_destroy_listener {

tests/display-test.c

@@ -32,8 +32,8 @@
 #include <sys/types.h>
 #include <sys/stat.h>
 
-#include "wayland-server.h"
 #include "wayland-private.h"
+#include "wayland-server.h"
 #include "test-runner.h"
 
 struct display_destroy_listener {

tests/event-loop-test.c

@@ -25,8 +25,9 @@
 #include <assert.h>
 #include <unistd.h>
 #include <signal.h>
-#include "wayland-server.h"
+
 #include "wayland-private.h"
+#include "wayland-server.h"
 #include "test-runner.h"
 
 static int