[wpimath] Add PIDController::GetTotalError and ProfiledPIDController::GetTotalError

[itsmeft24]

Adds the ability to retrieve the accumulated error from both PIDController and ProfiledPIDController to allow for the user to monitor the outputs of each individual term.

[calcmogul]

Keep in mind you should avoid the I term. The most common cause of steady-state error is modeled disturbances. Feedforward can compensate for that immediately, whereas pure integral control has to wind up and down. Integral control should only be used for unmodeled/unmodelable disturbances, and even then, it should only integrate the difference between the expected and actual plant state, not the difference between the setpoint and plant state.