Dual Extrusion: Bed leveling assumes fixed values for height

[brvdboss]

When using the dual extrusion print head, the firmware makes the assumption that the bed is beloz 50mm

https://github.com/Snapmaker/Snapmaker2-Controller/blob/3150c90a17f5eccc3f1c078a7d13439d6a5e97ca/snapmaker/src/service/bed_level.cpp#L39 https://github.com/Snapmaker/Snapmaker2-Controller/blob/c92df5047555307b14c078fd3080636f9bf6727f/Marlin/Configuration.h#L1239

I think both defines have the same intention.

When for some reason, the bed is higher, this blocks the calibration procedure: https://forum.snapmaker.com/t/dual-extruder-stuck-in-bed-level-calibration/30640 https://youtu.be/Usff7Z2fSm0

Because I created a custom easy bed switching mechanism, the thickness of the bed is higher, and this triggers an error. Increasing that value to 100mm solves the issue for now. However this doesn't solve the core issue. The actual value should be triggered by the probe, not be an arbitrary value.

This issue breaks down in two main problems:

• The value is arbitrary and should not be hardcoded (ideally)
• If it fails at this point in the calibration, the screen just hangs at the "calibrating" step and you're stuck

This is a similar issue as this one: https://github.com/Snapmaker/Snapmaker2-Controller/issues/27 That one was for the single extruder print head and has actually been solved. (so could be closed) A similar problem here occured again.