Support scanning analog Z probes

[T3P3]

Scanning code written and tested; calibration function still needs to be implemented

[dc42]

Calibration function is now supported. Testing TBD.

[dc42]

Other related issues before this can be considered complete:

1. Errors (e.g. amplitude errors) from the prove during scanning are not handled well - now fixed.
2. These probes don't continuously report their output (doing so over CAN would be expensive). Therefore the reading in the OM and DWC doesn't change except when M558.1 or G29 S1 is being run.
3. For the same reason, these probes can't currently be used as regular Z probes e.g for Z homing or bed tramming.

Possible fixes:

1. Send the probe reading over CAN e.g. every 250ms so that DWC and the OM stay fairly up to date
2. When processing M558.1, update the trigger threshold of the analog handle so that the probe can behave like a digital Z probe.