WindowServer: Implement fullscreen windows

If window size does not match framebuffer size, window data will be
scaled to framebuffer using nearest sampling for best performance.

userspace/libraries/LibGUI/include/LibGUI/Packet.h

@@ -164,6 +164,7 @@ namespace LibGUI
 		WindowSetAttributes,
 		WindowSetMouseCapture,
 		WindowSetSize,
+		WindowSetFullscreen,
 
 		DestroyWindowEvent,
 		CloseWindowEvent,
@@ -221,6 +222,11 @@ namespace LibGUI
 			uint32_t, height
 		);
 
+		DEFINE_PACKET(
+			WindowSetFullscreen,
+			bool, fullscreen
+		);
+
 	}
 
 	namespace EventPacket

userspace/libraries/LibGUI/include/LibGUI/Window.h

@@ -61,6 +61,7 @@ namespace LibGUI
 		void invalidate() { return invalidate(0, 0, width(), height()); }
 
 		void set_mouse_capture(bool captured);
+		void set_fullscreen(bool fullscreen);
 
 		void set_position(int32_t x, int32_t y);