Fixup leveling and other issues

Parentheses need here otherwise sanitycheck.h does wrong thing on line 222

Give all temp arrays 4 indices

- Also patch up some warnings

- Fix a bug reading `code_value` for `M503 Sn`
- Hide and remove unused variables

Latest upstream commits

Always 4 temp sensors

- Also a small tweak to SanityCheck.h

Avoid warnings in SanitiCheck.h

First aid for #1703

- Increase the probe offset range to -20…20
- Apply the range limits to the menu item

/SanityCheck.h:107:53: warning: missing terminating ' character
...

to avoid:
Marlin_main.cpp:1790: warning: array subscript is above array bounds.

Clean "fromsd" array if not SDSUPPORT

- Put + in front of positive values in the output

Instructions for Mesh Bed Leveling

Latest upstream commits

comment #define Z_DUAL_STEPPER_DRIVERS

Latest upstream commits

Move definition of PIDdT back to temperature.h

Don’t set CUSTOM_M_CODE_SET_Z_PROBE_OFFSET if there’s no Z probe

- Make `zprobe_zoffset` conditional
- Fix ConfigurationStore for `zprobe_zoffset`

- Init `zprobe_zoffset`
- Remove `current_position[Z_AXIS] = zprobe_zoffset` lines from the
`set_bed_level_equation_*` functions
- Apply standards to `mesh_bed_leveling` files
- Document `MESH_BED_LEVELING`

Fix MAX6675 again and introduce set_current_temp_raw()

if not have SDSUPPORT the fromsd array is not necessary