WindowServer: Implement partial window resizing

This patch adds support for client side resizing, so clients can request
the server to resize their windows. WindowServer will respond with
resize event when and if the resizing is complete.

userspace/programs/WindowServer/main.cpp

@@ -354,6 +354,10 @@ int main()
 						if (auto ret = LibGUI::WindowPacket::WindowSetMouseCapture::deserialize(client_data.packet_buffer.span()); !ret.is_error())
 							window_server.on_window_set_mouse_capture(fd, ret.release_value());
 						break;
+					case LibGUI::PacketType::WindowSetSize:
+						if (auto ret = LibGUI::WindowPacket::WindowSetSize::deserialize(client_data.packet_buffer.span()); !ret.is_error())
+							window_server.on_window_set_size(fd, ret.release_value());
+						break;
 					default:
 						dprintln("unhandled packet type: {}", *reinterpret_cast<uint32_t*>(client_data.packet_buffer.data()));
 				}