Implement G60 / G61 to meet spec

[karcaw]

This Fixes the case where no Integers were specified on the G61 command:

G60
G0 X100 Y100 Z20
G61 X Y  

does not return to the last location as :

G60
G0 X100 Y100 Z20
G61 X0 Y0

does. this matches what the spec says:
https://marlinfw.org/docs/gcode/G061.html
which does not even document you can put an integer after the axis letters.

Description

Fix for #26222

Requirements

No

Benefits

G61 will work according to the spec.

Configurations

Related Issues

(#26222)

[thinkyhead]

It may be that the implementation of G61 itself has been wrong from the start. Also, we don't have a clear specification for applying G61 E<num>. Also, it is notable that the RepRap wiki has no entry for this G-code. So we'll need to look at the specification and implementation in some other firmwares, and also see how our G60 compares to some others.

[thinkyhead]

At first glance, it appears our G61 is intended to work just like G60 Q in other firmwares.

[thinkyhead]

I went ahead and modified G60 to match the description from the RepRap wiki, and added a note to the wiki about the offsets. I also added G61 to the wiki. I'll be sure to update our own G60 / G61 documentation once this is merged.