Need constructor for struct types such as pose_3d and shape

Ability to declare & define struct typed parameters in a single line is much easier that defining them using keep constraints. And we need constructors to be able to do that. For Example

speed_shape_1: common_speed_shape(rate_profile: constant, rate_peak: 10mpss, target: 50kph)

pose1: pose_3d(position.x: 10.8936m, position.y: -30.7277m, position.z: 0m, orientation.roll: 0rad, orientation.pitch: 0rad, orientation.yaw: 1.82177rad)