Implement AVR Platform

Addressing #6992 and #5851

* Remove ADVANCED_PAUSE_FEATURE requirement for PROBING_HEATERS_OFF

* Add HEATER_IDLE_HANDLER conditional

Removing redundant_temperature from public section and leaving it in the
private section

* Unify M600 and M125 pause features
* Cleanup per thinkyhead's comments
* Rename filament_change_menu_response to advanced_pause_menu_response
* Include HAS_BED_PROBE in QUIET_PROBING
* Update gMax example file
* is_idle() is out of scope without the braces
* Convert FT-i3-2020 to Advance Pause names...
* Allow pause even if not printing

 - rename to PROBING_HEATERS_OFF
 - move heater pausing functionality into thermalManager
   - add variables, pause(), ispaused(), other functions
 - add fan pausing functionality -> PROBING_FANS_OFF
 - add probing_pause() wrapper
 - move pausing into do_homing_move() and do_probe_move() to minimize quiet time and so other probe types can benefit
 - example configs

also removed wayward 'address of' ampersand in setTargetHotend and setTargetBed parameters

If Marlin is inside the temperature ISR, the stepper ISR is enabled. If
a stepper event is now happening Marlin will proceed with the stepper
ISR. Now, at the end of the stepper ISR, the temperatre ISR gets enabled
again. While Marlin proceed the rest of the temperature ISR, it's now
vulnerable to a second ISR call.

Also lined up the >> 1 and / 2 mentioned earlier in the unconstrained I term issue,

Also improve the documentation of this and related options, and set
EXTRUDE_MINTEMP to 170 everywhere.