Followup for #13013

Followup to #13703

- Save and restore workspace offsets
- Add retract and purge (hidden) options
- Always restore axis relative modes
- Use added `G92.9` to do position restores

The real fix. PR #13568 was wrong.

Add option to move away from endstop after homing.
- Add `ENDSTOP_BACKOFF` for printers with a recessed Z home button (Lulzbot TAZ 6).
- Also prevents chattering when sensorless homing with axes against bumpers.

Followup to #13531

- Only save to PLR file on moves with E and X or Y
- Save to PLR after any long-ish Z downward move

Allow `ENABLED`, `DISABLED`, `PIN_EXISTS`, and `BUTTON_EXISTS` to take multiple arguments. Also add:
- Alias `ANY(...)` for `!DISABLED(...)`
- Alias `ANY_PIN(...)` for `PIN_EXISTS(a) || PIN_EXISTS(b) ...`
- Alias `EITHER(A,B)` for `ANY(...)`
- Alias `ALL(...)` and `BOTH(A,B)` for `ENABLED(...)`
- `NONE(...)` for `DISABLED(...)`

Reference: #13380

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

* 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)

The chances of a 10° overshoot is pretty minimal.

- 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.