wl_compositor: implement version 7

wire/wl_compositor.txt

@@ -5,3 +5,6 @@ request create_surface {
 request create_region {
     id: id(wl_region) (new),
 }
+
+request release (destructor, since = 7) {
+}

wire/wl_surface.txt

@@ -64,3 +64,7 @@ event preferred_buffer_scale (since = 6) {
 event preferred_buffer_transform (since = 6) {
     transform: u32,
 }
+
+request get_release (since = 7) {
+    callback: id(wl_callback) (new),
+}