Refresh Marlin git helper scripts

- `mfadd` adds and fetches a user’s fork of Marlin
- `mfqp` invokes `git commit -m`, `mfrb`, `git push -f`

FLSUN and trailing whitespace cleanup

Add and apply interrupt helper macros

Cleanup after some direct commits

Fix double definition in configuration_store

https://github.com/MarlinFirmware/Marlin/commit/5e9726530f
ac1b9437c2

M43 Toggle & Z servo test - fix bug & add another check

Add Linear Advance values to EEPROM and LCD

Fix Makefile build

- use volatile for registers
- avoid implicit casts

Only queue babysteps if axis is in a known position

Identifed a display initialization issue.

This data corruption problem is very difficult.  Just changing the code
a little bit changes whether the problem even happens and what is
affected.  I need these changes in the main branch so I can operate with
the extra debug code always available and turned on.

Everything is setup such that if M100 is turned off or DEBUG(ECHO) is
turned off, the code is not affected.   M100 has been made a little bit
more inteligent so it can display the serial command buffers in a more
meaningful way (because the data corruption seems to often times end up
in that area).

Show Cancel/Continue screen for ABL "Level Bed"

Clean up endstop triggering code

Fix softspi variant conditional for 1284p

Fix undefined symbol if DOUBLECLICK_FOR_Z_BABYSTEPPING and HAS_BED_PROBE defined

spi.h is only needed if HEATER_0_USES_MAX6675 is defined, so making its inclusion conditional on HEATER_0_USES_MAX6675 being defined.