add xdg decoration, scene/tree factories, geometry + seat focus

more wrapper soup. xdg decoration manager, scene/tree node factories so
callers stop touching raw wlr_scene_*_create, a box geometry helper, and
seat pointer/keyboard focus clearing. dragging myself through it.

include/wlr/output.hpp

@@ -19,6 +19,11 @@ public:
 	const char* make() const { return m_output->make; }
 	const char* model() const { return m_output->model; }
 
+	int width() const { return m_output->width; }
+	int height() const { return m_output->height; }
+	enum wl_output_transform transform() const { return m_output->transform; }
+	struct wlr_output_mode* current_mode() const { return m_output->current_mode; }
+
 	struct wlr_output_mode* preferred_mode() const {
 		return wlr_output_preferred_mode(m_output);
 	}
@@ -32,6 +37,15 @@ public:
 		wlr_output_state_finish(&state);
 		return ok;
 	}
+	bool set_mode(struct wlr_output_mode* mode) {
+		if (!mode) return false;
+		struct wlr_output_state state;
+		wlr_output_state_init(&state);
+		wlr_output_state_set_mode(&state, mode);
+		bool ok = wlr_output_commit_state(m_output, &state);
+		wlr_output_state_finish(&state);
+		return ok;
+	}
 
 private:
 	struct wlr_output* m_output;