Minimum distance field does not update when value changes

[oktophonie]

Describe the bug
Adjusting the offsets of an item can result in the 'Minimum distance' value for the item changing automatically in order to allow the item to approach or overlap other elements. However, the value does not automatically update in the Properties panel.

See: #13246 (comment)

To Reproduce
Steps to reproduce the behaviour:

1. Create an item, e.g. a piece of Stave Text. Open the 'Appearance' popup in the Properties panel. The default Y-offset is -1; the minimum distance is 0.5.
2. Click the up arrow to change the Y-offset to -0.5. The minimum distance is shown as 0.5, but has actually become 0.4. If you deselect then reselect the text item, and open the 'Appearance' popup, you will see the correct value.
3. Click the up arrow again to change the Y-offset to 0. The minimum distance will still be shown as 0.4 (or 0.5); but the real value is now -999 (meaning, effectively, 'disabled' - as the text item is now in contact with the stave).

Note, incidentally, that the display of the 'Leading space' changes from 0 to 0.00 when this final adjustment is made (also not ideal).

box-220909-1028-45.mp4

Expected behaviour
The 'Minimum distance' field should always show the current value, even when this value has changed indirectly. (This was, apparently, a technical impossibility in the old UI.)

Note
This is a spinoff from #13246 and would appear to be related to #11637.