Wait for smooth scrolling animation to add new message (#2084)

Co-authored-by: Paweł <zneix@zneix.eu>
Co-authored-by: pajlada <rasmus.karlsson@pajlada.com>

src/widgets/Scrollbar.hpp

@@ -44,6 +44,8 @@ public:
     qreal getDesiredValue() const;
     qreal getCurrentValue() const;
 
+    const QPropertyAnimation &getCurrentValueAnimation() const;
+
     // offset the desired value without breaking smooth scolling
     void offset(qreal value);
     pajlada::Signals::NoArgSignal &getCurrentValueChanged();