- Also implemented real endstop reading on interrupt.

- Fixed the planner incorrectly avoiding optimization of the block following the active one.
- Added extra conditions to terminate planner early and avoid redundant computations.

Allows the Stepper ISR to wait until a given block is free for use. Allows Planner to plan the first move, which is split into two.

Better encapsulation and considerably reduce stepper jitter

Use macros that explicitly avoid double-evaluation and can be used for any datatype, replacing `min`, `max`, `abs`, `fabs`, `labs`, and `FABS`.

Co-Authored-By: ejtagle <ejtagle@hotmail.com>

Co-Authored-By: ejtagle <ejtagle@hotmail.com>

Enable 6th-order jerk-controlled motion planning in real-time.
Only for 32bit MCUs. (AVR simply does not have enough processing power for this!)

This ensures that steppers that share an enable pin will only be disabled for a miniscule time.

* Automatically reset stepper timeout in manage_inactivity

Any code that adds moves to the planner can skip resetting the stepper timeout. We can let `idle` / `manage_inactivity` reset the timer whenever it detects any moves in the planner.

* blocks_queued => has_blocks_queued

Fix #10004

From #9914 by @Sebastianv650

See https://github.com/MarlinFirmware/Marlin/issues/9852#issuecomment-369861822

Followup to #9503

This reverts commit 4e891e9fb7.

Reverting commit 3cd7659

Also remove unused grid slicing function when using UBL segmented.