Reference #13156

Reference #13250

Addressing #13231

Ticket #13228

If `INCH_MODE_SUPPORT` is undefined, G20 is an unknown command as it should be (Marlin is, by default, operating in metric mode). G21, however, is found in many slicers and printer start gcode sections and should be accepted (as a NOOP) to avoid the unknown commands.

Fix #12643
Only factors above 1 can have a 'positive' effect.

Co-Authored-By: shitcreek <45380455+shitcreek@users.noreply.github.com>

Fix #9799 — hopefully not a unicorn

Fix #13184

See #8010

See #13000

See #13065

Observing from the console, it makes the most sense to do `//action:probe_retry` before executing commands.