[3DEX] x y axis calibration

Update note:

V2 version:
change height to 5mm , hope can keep some wires.
and change corner switch to avoid overflow.
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When using xyz axis printer , X and Y axis are the most need for calibration ,I draw a simple cad for calibration.

you can easier use the distance to calculate
"extrusion flow" & "x y step"

use the result to change your marlin to accurate your 3D printer now!!

enjoy it~