Adds the specified amounts to all targets' velocities. A positive x velocity is in the direction that the target is facing, while a positive y velocity is downward on the screen.

Required parameters:

- none

Optional parameters:

- x = x_value (float)
  Specifies the value to add to the x-velocity of the target.
- y = y_value (float)
  Specifies the value to add to the y-velocity of the target.
- ID = target_id (int)
  Specifies the desired target ID to affect. Only targets with this target ID will be affected. Defaults to -1 (affects all targets.)

Examples:

`; Applies constant gravity to all targets
type = TargetVelAdd
trigger1 = 1
y = 0.45`