Reference: #13380

See https://github.com/pinchies/Marlin/pull/1#issuecomment-471388743

See commentary at #11623

* Multi-nozzle selective duplication
* Use a bit-mask, reduce stepper_indirection.h size
* Tweak the multi-nozzle duplication description
* Use 'S' as a bool in M605
* Add HAS_DUPLICATION_MODE conditional
* Remove '_MODE' from the option name
* M605 in the style of Stacker M280
* Also include direct mask style (P)

As mentioned in #13370

The chances of a 10° overshoot is pretty minimal.

Originally #13344

Add support for printers with inverted fan pins by adding `#define FAN_INVERTING 1` to `Configuration_adv.h` and modifying the fan write macros.

Should fix "spontanous heating" problems due to order of operations error. Error occurs at least with ststm32 v5.1.0 in PlatformIO.

Followup to #12201

- Send notifications to ExtUI for M0/M1

- wait_for_user can be non-volatile (not changed by interrupt)
  C / C++ compilers don't optimize away reads of non-volatile variables when a function call is used between accesses, because *any* variable could be changed by the function call. Since `wait_for_user` can't be changed without a function call, it should be non-volatile so the compiler can optimize away cases where it is read more than once without an intervening function call.

- Ensure `MarlinUI:get_progress` is defined for `ExtUI`.
- Fix for `BACKLASH_SMOOTHING` with small segments.
  `BACKLASH_SMOOTHING` with extremely small segments failed to fully correct due to the correction factor being rounded down. Rounding up ensures the entire backlash will converge to zero even for small segments.
- Add pinout for the beta revision `EINSY_RETRO`.
- Update soft endstops with tool offsets (for toolchange et. al. move clamping) (#12568)

Fix #13333