.) Use already existing inverse_millimeters instead of /
block->millimeters.
.) Prevent overflow during acceleration calculation by checking if float
is necessary. Idea modified from Sailfish.
.) Save two uint32_t or even float multiplications by checking if
step[AXIS] has steps and if max acceleration is lower than accel. If
not, there is no need to check this axis.

We don't want to have retract/prime movements done with LIN_ADVANCE, that's also true with simultaneously executed Z-hops.

・Add forgotten '\'

…and apply const to some method parameters

Use to sync the planner after an interrupted move (when not overriding
the logical position).

This is in advance of moving non-linear bed leveling to the planner
class.

Use lx, ly, lz for “logical” positions

Follow-up to #4666

Also improve the documentation of this and related options, and set
EXTRUDE_MINTEMP to 170 everywhere.