Generic_Grbl And Generic_LinuxCNC missing commands in 26.3

By default the Generic_Grbl And Generic_LinuxCNC error out on G20,G21 and G43 commands when post processing files with those machines.
The post processors include those commands.

It appears they were written by an earlier version of the machine formatting and need updated

The issue can be temporarily fixed by adding the offending commands to the list of supported commands, however, I have not created a pull request as it sounds like there might be further changes to the machine configuration standard before the full release.

Start by inspecting the Generic_Grbl and Generic_LinuxCNC machine configurations and the post processors that emit G20, G21, and G43. Reproduce post processing with those machines, then confirm the supported-command handling and the machine configuration standard before deciding what needs updating. Done means valid files no longer error on these commands under the intended standard.

Written by the indexing model from the issue text.