feat: Add anti aliasing to the drawing of preview window

as title

pms: BUG-285265

Author: mhduiy

panels/dock/taskmanager/x11preview.cpp

@@ -265,6 +265,7 @@ class AppItemWindowDeletegate : public QAbstractItemDelegate
 
             DStyleHelper dstyle(m_listView->style());
             const int radius = dstyle.pixelMetric(DStyle::PM_FrameRadius);
+            painter->setRenderHint(QPainter::Antialiasing);
 
             painter->save();
             painter->setPen(Qt::NoPen);