Implement a validation check for the BLTouch

[slowbro]

Description

Checks the status() of the BLTouch when stowed/deployed before homing z and fails homing if they don't differ. Can successfully detect a) unplugged BLTouch probe pins, and b) reversed BLTouch probe pins.

Requirements

BLTOUCH, Z_SAFE_HOMING, BLTOUCH_VALIDATE_ON_HOMING

Benefits

Adds a safety check to homing for unplugged or reversed BLTouch probe wires.

Configurations

See requirements.

Related Issues

#24933

[thinkyhead]

With probe behavior now moved more into the Probe class, it may make more sense to do the validation check on every initial deploy of the probe, instead of just in the middle of G28 homing of Z.

[cfcgreg]

I noticed that was used with bug-fix 2.0x. Does it work with 2.1.2.1?

[sjasonsmith]

Based on the age of this PR and the lack of response to the last two comments, I'm going to close this out.

@slowbro you are welcome to resubmit this against the current bugfix-2.1.x branch if you are still interested. Per thinkyhead's earlier comment you would want to do that in the Probe class, so it would apply to every deploy of the probe and not only during homing.

Of course given the age of the PR I'm not sure whether this type of capability has already been implemented elsewhere.