Don't animate TreeView expansions

Some styles set a QStyle::SH_Widget_Animation_Duration. An animation
does not go well with just-in-time population of the expanded content.
This change avoids that for all TreeViews.

Fixes: QTCREATORBUG-24834
Change-Id: I16ca4c61733d8875e713d7349ed6b99ba37ecf74
Reviewed-by: Eike Ziller <eike.ziller@qt.io>
Reviewed-by: hjk <hjk@qt.io>

src/plugins/coreplugin/manhattanstyle.cpp

@@ -387,6 +387,10 @@ int ManhattanStyle::styleHint(StyleHint hint, const QStyleOption *option, const
         if (Utils::HostOsInfo::isMacHost())
             ret = QFormLayout::AllNonFixedFieldsGrow;
         break;
+    case QStyle::SH_Widget_Animation_Duration:
+        if (widget->inherits("QTreeView"))
+            ret = 0;
+        break;
     default:
         break;
     }