updateInputField(obj, prop, widget) ... update obj's property prop with the value of widget.
The property's value is only assigned if the new value differs from the current value.
This prevents onChanged notifications where the value didn't actually change.
Gui::InputField and Gui::QuantitySpinBox widgets are supported - and the property can
be of type Quantity or Float.
If onBeforeChange is specified it is called before a new value is assigned to the property.
Returns True if a new value was assigned, False otherwise (new value is the same as the current).
Referenced by PathScripts.PathGui.QuantitySpinBox.updateProperty().