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

No more mystery halts & resets

Moved messages to language.h

Added current command to inactive timeout message

Add check for Turkish Font before setting better font for graphic displays

・Remove all the #ifndef
・Follow the PR #4603 (Strip never-translated strings from language
files)
・Follow the PR #4634 (Set language display charset in language.h)
・Follow the PR #4936 (Put max_jerk vars in array, clean up jerk code)
・Adjust spacing

Add an emergency-command parser to MarlinSerial's RX interrupt.

The parser tries to find and execute M108,M112,M410 before the commands disappear in the RX-buffer.

To avoid false positives for M117, comments and commands followed by filenames (M23, M28, M30, M32, M33) are filtered.

This enables Marlin to receive and react on the Emergency command at all times - regardless of whether the buffers are full or not. It remains to convince hosts to send the commands. To inform the hosts about the new feature a new entry in the M115-report was made. "`EMERGENCY_CODES:M112,M108,M410;`".

The parser is fast. It only ever needs two switch decisions and one assignment of the new state for every character.

One problem remains. If the host has sent an incomplete line before sending an emergency command the emergency command could be omitted when the parser is in `state_IGNORE`.
In that case the host should send "\ncommand\n"

Also introduces M108 to break the waiting for the heaters in M109, M190 and M303.

Rename `cancel_heatup` to `wait_for_heatup` to better see the purpose.

Extend M421 with I and J parameters

Addressing #3325 – Avoid undefined symbol errors in the compiler.

Redo of #3268 by @jbrazio

Following up on #3231

documentation/LCDLanguageFont.md moved to http://www.marlinfirmware.org/ at commit 12d0983757,
but http://www.marlinfirmware.org/ isn't working.