Fixes #6426

Fixes #6445

Also...   The memory corruption issue may be fixed.   The GCC compiler
was inlining static functions and this caused the G29() stack frame to
become much larger than the AVR could handle.

Patch fastio.h with Timer 2 interrupt support

* relocated ubl state to config. store:
 * removed a number of ubl state variables and padding which were largely unused - saved 58 bytes of both SRAM and EEPROM;
 * modified ubl sanity_check - no longer checks removed state variables that were otherwise unused, where checking didn't seem to accomplish anything, ultimately;
 * removed pre_initialized state, saving 64 bytes of SRAM;
 * removed automatic saving of UBL state after UBL activation/deactivation;
* consolidated multiple GRID_MAX_POINTS_X/Y to 'Global Leveling' section of EEPROM;
* minor update to G29 Sx notes/instructions;
* renamed mesh load and save parameter to 'slot' from 'm' for clarity;

fix maximum mesh_index_ array size at 16 (15+1);

Minor cleanup, optimize number-to-string

Add polish font for GLCD displays only.
HD44780 work properly without polish character.
Update language_pl.h.

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