Gui: if an expression is set for Euler angles in the placement dialog then evaluate the expression instead of determining the angles from the rotation

See forum thread: https://forum.freecadweb.org/viewtopic.php?f=3&t=72522

src/Gui/QuantitySpinBox.cpp

@@ -417,6 +417,13 @@ QString Gui::QuantitySpinBox::expressionText() const
     return QString();
 }
 
+void QuantitySpinBox::evaluateExpression()
+{
+    if (isBound() && getExpression()) {
+        showValidExpression(Number::SetIfNumber);
+    }
+}
+
 void Gui::QuantitySpinBox::setNumberExpression(App::NumberExpression* expr)
 {
     lineEdit()->setText(getUserString(expr->getQuantity()));