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.

Derived from
https://github.com/AnHardt/Marlin/commit/6e8ede8c69
7f8d8e0dd

Make sure to only set the fan state once when extruders share a fan

Addressing #3743

Fix compilation error in Thermal Runaway debugging code

When setting the bed temp via M140/M190 if the thermistor does not read an increase of WATCH_BED_TEMP_INCREASE degrees by WATCH_BED_TEMP_PERIOD seconds then it will throw "Error:Heating failed, system stopped! Heater_ID: bed" and call the kill() function.

Conflicts:
	Marlin/Configuration_adv.h

As noted by @FalloutBe in #3519

・Add more "UL" suffix
・Restore removed "UL" suffix

Only measure and store filament width when E is going forward.

Following up on #3231

Fixes for #3189

Setting a temp is still missing

Adds the parameter U to M303. If U1 is included , it will use the
PID-values from the auto-tune.

Addition to #3140

Addressing #3085. If the target_temperature is set directly it never invokes or disables the timer set in `start_watching_heater`, so after _stopping a print_ or turning off _all heaters_ you could get a “Heating failed” error.