Respect MANUAL_PROBE_START_Z in UBL

[sjasonsmith]

Description

PROBE_MANUALLY and UBL have a complex relationship. Enabling UBL implicitly disables PROBE_MANUALLY, because UBL has its own manual probing mechanism.

Unfortunately this also causes the MANUAL_PROBE_START_Z to be ignored, since it wasn't originally added to UBL.

This change modified UBL to use MANUAL_PROBE_START_Z, and falls back to Z_CLEARANCE_BETWEEN_PROBES if it is available.

Benefits

Allows users to reduce the amount of time they spend spinning their encoder wheels!

Configurations

The following configs are for use in the simulator. Real configs are available from the referenced issue.
Marlin.zip

Related Issues

#19795 - UBL with PROBE_MANUALLY doesn't lower to MANUAL_PROBE_START_Z and stays at Z_CLEARANCE_BETWEEN_PROBES

[sjasonsmith]

@Roxy-3D, do have any reason to NOT want UBL to respect MANUAL_PROBE_START_Z if present?

[sjasonsmith]

I want to avoid merging this until I examing how it is related to #19804. It seems closely related to this, and maybe some additional adjustments are needed.

[pinchies]

Ironic that this fix for UBL, saving people their encoder wheels, for people using MBL it actually caused people to have to spin their encoder wheels more at every point! #facepalm #21239

[thinkyhead]

Is it this which is having the unwanted effect?

#if !defined(MANUAL_PROBE_START_Z) && defined(Z_CLEARANCE_BETWEEN_PROBES)
   #define MANUAL_PROBE_START_Z Z_CLEARANCE_BETWEEN_PROBES
 #endif

And so, is it only problematic when MANUAL_PROBE_START_Z is not defined? The idea was to provide some kind of value based on the config that would be known to be safe. Maybe there is a smaller value supplied in the config which would make a better default.