single-pixel-buffer: make wl_global public

I wish to use a allowlist of globals for my security context
implementation rather than a blocklist, which means I need access to
the wp_single_pixel_buffer_manager_v1 global in order to allowlist it.

I think using a allowlist will make it harder for me to accidentally
expose globals to a security context that were meant to be restricted.

include/wlr/types/wlr_single_pixel_buffer_v1.h

@@ -11,7 +11,14 @@
 
 #include <wayland-server-core.h>
 
-struct wlr_single_pixel_buffer_manager_v1;
+struct wlr_single_pixel_buffer_manager_v1 {
+	struct wl_global *global;
+
+	// private state
+
+	struct wl_listener display_destroy;
+};
+
 
 struct wlr_single_pixel_buffer_manager_v1 *wlr_single_pixel_buffer_manager_v1_create(
 	struct wl_display *display);

types/wlr_single_pixel_buffer_v1.c

@@ -8,12 +8,6 @@
 
 #define SINGLE_PIXEL_MANAGER_VERSION 1
 
-struct wlr_single_pixel_buffer_manager_v1 {
-	struct wl_global *global;
-
-	struct wl_listener display_destroy;
-};
-
 struct wlr_single_pixel_buffer_v1 {
 	struct wlr_buffer base;
 	struct wl_resource *resource;