Fix #11872

- Move FWRETRACT to the planner
- Combine leveling, skew, etc. in a single modifier method
- Have kinematic and non-kinematic moves call one planner method

See https://github.com/MarlinFirmware/Marlin/issues/11103#issuecomment-421387611

Co-Authored-By: tcm0116 <tcm0116@users.noreply.github.com>

Values taken from Zonestar firmware for P802QA with a Melzi board. Timestamps from the firmware package are from April 2016.

`MAX_SERVOS` => `NUM_SERVO_PLUGS`

When possible, make `active_extruder` a `constexpr` to save some PROGMEM.

Fix #11697

On many IDEX machines the allowed travel of the X1 carraige and X2 carraige does not perfectly overlap.

This helps the issue.   But more work needs to be done at the higher level.  (For example the X1_MAX_POS should probably be factored into G26's mesh validation pattern.)

Co-Authored-By: teemuatlut <teemu.mantykallio@live.fi>

- Clean up the API to use a `static` class instance to adhere to Marlin convention
- Add `const` position data access for read/write
- Add Storage capacity to the interface

agData in Table 71 is extremely oversampled (see Issue #11220). I have removed the data points that perform *worse* than linearly interpolating the remaining points, and fixed up two points that were simply rounded incorrectly.

Co-Authored-By: Aaron Griffith <aargri@gmail.com>