Also added the new .pio-related directory to .gitignore, and a few ignores for those who use cmake.

* Correct over optimization of pre-initialized variables

NEAR_ZERO() works most of the time...  But it leaves corner cases
uncovered.  We need to explicitly check if these variables are +/-
infinity.

* Correct over optimization of pre-initialized variables

Last three Spanish language strings

Updates as per @thinkyhead request.

Update language_de.h

* Update language_cz.h for new translations

* Correction translate

* Revert correction back to hotend

Adding missing strings to Spanish language, as per changes recently
done to the RCBugFix branch.

updated the RCbugfix release with additional Dutch translations

The first character in the string wasn't blanked if the number went from >= 100 to <100, resulting in artefacts in the displayed string.

The Configuration.h file entries for BL-Touch have been updated to:
```cpp
//#define BLTOUCH
//#define BLTOUCH_DELAY 375      // (ms) Enable and increase if needed
//#define BLTOUCH_HEATERS_OFF // if defined the printer's heaters are
turned off during probe event
```

The electro-magnetic interference from the bed and nozzle are affecting
the BL-Touch repeatability for some users.   This problem can be helped
by shutting down the heaters during the actual probe event and then
quickly turning them back on.

Because this code is messing with the heaters, it is written in a
paranoid manner.  It only turns the heaters back on if everything is
EXACTLY as it expects things to be.  The BL-Touch probe must have been
put into a deployed state less than 20 seconds prior, or the stow()
function will NOT turn the heaters on.

This code has been tested and works for both G28 and probing functions.

Also setting up Z-Probe on the machine.

Minor cleanups, work-in-progress

Change to support new name GRID_MAX_POINTS_XY
Start UBL at version 1.0 in the CUSTOM_MACHINE_NAME

These are my two 'Nice' machines.  Both are good example machines.  The
FolgerTech i3-2020 is probably the best value kit on the market right
now.  And it has developed a 'Cult Following' of hobbiests.  I'll always
have an up to date Configuration.h file set for it, so it may as well be
an example configuration.

And the gCreate gMax 1.5+ is the best printer I've ever seen that runs
Marlin.  For sure, I'll always have up to the minute Configuration.h
files for this printer also.   I've moved over to using the gMax as my
primary development machine for Marlin.   So...  Besides being a good
machine, it is a nice convienience for me to have this Configuration.h
file as an 'Example'.

Fixes #6393

There are some quite tricky ones which are hardly translateable.
Maybe @Sebastianv650 can review this

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