The offset for Z_DUAL_ENDSTOP (z_endstop_adj) is already in Marlin.
This PR just makes it a configuration item.

z_endstop_adj is initialized in two places so both had to be modified.

I've just uploaded a major change to pinsDebug.
The big change was creating an array in FLASH that contained every
active pin definition. That reduced the RAM memory usage considerably
but increased the FLASH usage.
Creating the array requires going through the pin list twice. Rather
than having two copies of it in the code I moved the list out to another
file (pinsDebug_list.h) and then just did two #includes.
From the user’s view they’ll see the following changes:
1. Now reports all the names assigned to a pin
2. The port is now reported in addition to the pin number.
3. When PWM0A & PWM1C share a pin, both PWMs are reported
4. More PWM/Timer info is reported
One new item that may cause some concern is the usage of the LINE
predefined preprocessor macro. It may not be available if the Arduino
IDE goes to a different compiler.

Includes support for 1284 & 1286 families.

Memory usage changes when enabling PINS_DEBUGGING:
ATmega2560
FLASH
.           without   52576
.           with new  64592
.           with old  62826
.           new-out   12016
.           old-out   10250
.           new-old   1766
.
RAM
.           without   2807
.           with new  2875
.           with old  3545
.           new-out   68
.           old-out   738
.           new-old   -670

==================================================================

minor changes - mostly formatting

1) added newline to end of teensyduino file

2) changed flag name from TEENSYDUINO to TEENSYDUINO_IDE.  Got warnings
about redefining TEENSYDUINO

3) removed some trailing spaces

reduce PROGMEM size & update pin list

Reduced PROGMEM usage by
1) converting often used macro to a function
2) moved as much as possible into the function

This required creating two arrays of address pointers for the PWM
registers.

==================================================================

update with new M3, M4, M5 pin names

==================================================================

report I/O status for unused/unknown pins

The fix in #6251 for bilinear Z offset was flawed and broke the Z parameter of G29 for bilinear levelling.  This is reverted and a different fix is used for the double-addition of the Z-probe offset to the bilinear correction grid.

Since run_probe was altered to return the probe Z position rather than the nozzle Z position bilinear levelling has been broken because the Z-offset has been applied twice - once in the run_probe function, and then again in the G29 code for bilinear levelling.

M421 was not connected up for AUTO_BED_LEVELING_BILINEAR.
M421 needed to migrate mesh data to new UBL EEPROM layout.

As it turns out...   an unsigned int can not go to less than 0,  so the
loop never terminates.