[GUI] Make precision of QuantitySpinBox accessible from Python

src/Gui/QuantitySpinBox.cpp

@@ -886,6 +886,7 @@ void QuantitySpinBox::stepBy(int steps)
     }
 
     Quantity quant(val, d->unitStr.toStdString());
+    quant.setFormat(d->quantity.getFormat());
     updateText(quant);
     updateFromCache(true);
     update();

src/Gui/QuantitySpinBox.h

@@ -46,6 +46,7 @@ class GuiExport QuantitySpinBox: public QAbstractSpinBox, public ExpressionSpinB
         double singleStep READ singleStep WRITE setSingleStep
     )  // clazy:exclude=qproperty-without-notify
     Q_PROPERTY(double rawValue READ rawValue WRITE setValue NOTIFY valueChanged)
+    Q_PROPERTY(double decimals READ decimals WRITE setDecimals)
     Q_PROPERTY(Base::Quantity value READ value WRITE setValue NOTIFY valueChanged USER true)
     Q_PROPERTY(
         QString binding READ boundToName WRITE setBoundToByName