fix(api): smoothie driver: Limit high currents to moving axes (#4729)

V1 habitually issues calls to the smoothie driver's move() function that include
only the axes that are going to move (basically because of the mover setup that
underpins motion control in V1). In V2, we have a unified source of control for
motor commands that always sends a full axis spec.

The smoothie driver was setting high currents for all axes specified in the
motion command, whether those axes moved or not. That meant that most of the
time, any command would set all axes to high currents. This is unnecessary,
generates heat, and may overstress the power supply, leading to unexpected skips
in certain high-friction situations.

Instead, use the code we already have to cut down on gcode command length to
determine which axes will actually move and only set those axes to high
currents.

Closes #4714