Help viewer: Add option for scroll wheel zooming

Fixes: QTCREATORBUG-14154
Change-Id: Ia6c4aedb78954614477f0228ba82c4dc476a2525
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@qt.io>
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/help/helpplugin.cpp

@@ -495,6 +495,9 @@ HelpViewer *HelpPlugin::createHelpViewer(qreal zoom)
 
     // initialize zoom
     viewer->setScale(zoom);
+    viewer->setScrollWheelZoomingEnabled(LocalHelpManager::isScrollWheelZoomingEnabled());
+    connect(LocalHelpManager::instance(), &LocalHelpManager::scrollWheelZoomingEnabledChanged,
+            viewer, &HelpViewer::setScrollWheelZoomingEnabled);
 
     // add find support
     auto agg = new Aggregation::Aggregate;