wlr_shm: 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 wl_shm 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_shm.h

@@ -22,7 +22,16 @@ struct wlr_renderer;
  * Currently, accessing two buffers concurrently via
  * wlr_buffer_begin_data_ptr_access() will return an error.
  */
-struct wlr_shm;
+struct wlr_shm {
+	struct wl_global *global;
+
+	// private state
+
+	uint32_t *formats;
+	size_t formats_len;
+
+	struct wl_listener display_destroy;
+};
 
 /**
  * Create the wl_shm global.

types/wlr_shm.c

@@ -23,14 +23,6 @@
 
 #define SHM_VERSION 1
 
-struct wlr_shm {
-	struct wl_global *global;
-	uint32_t *formats;
-	size_t formats_len;
-
-	struct wl_listener display_destroy;
-};
-
 struct wlr_shm_pool {
 	struct wl_resource *resource; // may be NULL
 	struct wlr_shm *shm;