The compiler may be able to optimize if it knows an array won’t be
changing.

`gcode_M84` only needs to call `finishAndDisableSteppers`, which calls
all the other functions.

- Documentation solution for #2476

Assuming #2470 fixed up the main issue.

- Update prepare_move_delta to take a target argument
- Add Delta support to plan_arc

Patch servos code for move

- Have `Servo::attach` explicitly return -1 if it fails
- Check for -1 in `Servo::move` because `servoIndex` might be 0
- Make `attach` / `detach` calls conditional on `SERVO_LEVELING`
- Move `SERVO_LEVELING` define to `Conditionals.h`

Elsewhere DRYRUN turns off the heating elements
and ignores constraints on them.

Here, whenever motion is entered into the planner,
if DRY RUN is set, we instantly act as if the E_AXIS
is in the desired final position.

to make clear - it's not a question but an order.