Some "fix-mounted" probes need manual stowing. And after probing some may prefer to raise or lower the nozzle. This restores an old option but tailors it to allow raise or lower as preferred.
With this option enabled, Z won't ever be raised until after `G28` has been completed, and it won't raise if Z becomes unknown. This is good for machines whose beds fall when Z is powered off.
If using babystep to adjust the Z probe offset, the axis will move and the mesh will be updated at the same time, causing a doubling of the Z offset over the rest of the print.
To correct for this, the current Z position would need to be modified in the opposite direction, canceling out the additional Z offset added to the mesh. This would be confusing to users, and moreover it would not be accurate without also taking the current Z fade level and current Z height into account.
It might make sense to change the mesh in the case where no babystepping is taking place, but this could be considered an undesirable side-effect of changing the `zprobe_zoffset`.
One way to remedy this would be to return to storing the mesh with `zprobe_zoffset` included, then subtracting `zprobe_zoffset` from the returned Z value. Thus, a babystep moving the Z axis up 1mm would subtract 1 from `zprobe_zoffset` while adding 1 to all mesh Z values.
Without including the `zprobe_zoffset` in the `z_values` there is no safe way to alter the mesh in conjunction with babystepping, although it's fine without it.
