Defines and uses set_setpoint_to_estimate() reusable function
Uses it in three places:
- axis.cpp to avoid transient on startup
- can_simple.cpp to avoid sudden movement upon mode change
- odrive-interface.yaml just to make it executable via USB and UART
Swaps set_input_pos() to set_input_pos_and_steps() so that we get the
same behavior when changing input_pos over USB and UART as we get when
we change it via CAN.