Fix #8890

Always honor minimum period on stepper pulse generation, and fix timing calculations

Signed-off-by: etagle <ejtagle@hotmail.com>

- Drop `max_jerk` with `JUNCTION_DEVIATION`
- Add `max_e_jerk_factor` for use by `LIN_ADVANCE`
- Recalculate `max_e_jerk_factor` when `junction_deviation_mm` changes
- Fix LCD editing of `junction_deviation_mm`

The timing value should be properly set for ALL boards. The compiler will check and set maximum step rate calculations based on those values.

- Stepper bugs fixed
- Support MIXING_EXTRUDER with Linear Advance
- Miscellaneous cleanup

* Misc fixes and improvements

- Get rid of most critical sections on the Serial port drivers for AVR and DUE. Proper usage of FIFOs should allow interrupts to stay enabled without harm to queuing and dequeuing.
  Also, with 8-bit indices (for AVR) and up to 32-bit indices (for ARM), there is no need to protect reads and writes to those indices.
- Simplify the XON/XOFF logic quite a bit. Much cleaner now (both for AVR and ARM)
- Prevent a race condition (edge case) that could happen when estimating the proper value for the stepper timer (by reading it) and writing the calculated value for the time to the next ISR by disabling interrupts in those critical and small sections of the code - The problem could lead to lost steps.
- Fix dual endstops not properly homing bug (maybe).

* Set position immediately when possible

- Respect axis max acceleration limits instead of forcing a fixed acceleration value.
- The `junction_unit_vec` ensures proper handling of entry and exit speeds even when the axes involved have different limits.

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

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

Fix #10777 for 2.0.x

Co-Authored-By: Ante Vukorepa <o.orcinus@gmail.com>

- Also implemented real endstop reading on interrupt.