Reduce usage of qApp in favor of static function calls

Q*Application classes have unusually many static functions. In many
cases in our code, these functions are unnecessarily called as instance
functions, using the qApp helper.

This patch replaces many occurencies of qApp with the according
Q*Application classname.

Change-Id: I6099a419fa7bf969891269c37ed7a9e817ef5124
Reviewed-by: hjk <hjk@qt.io>

src/plugins/help/helpplugin.cpp

@@ -136,9 +136,9 @@ bool HelpPlugin::initialize(const QStringList &arguments, QString *error)
         const QString &trFile = QLatin1String("assistant_") + locale;
         const QString &helpTrFile = QLatin1String("qt_help_") + locale;
         if (qtr->load(trFile, qtTrPath) || qtr->load(trFile, creatorTrPath))
-            qApp->installTranslator(qtr);
+            QCoreApplication::installTranslator(qtr);
         if (qhelptr->load(helpTrFile, qtTrPath) || qhelptr->load(helpTrFile, creatorTrPath))
-            qApp->installTranslator(qhelptr);
+            QCoreApplication::installTranslator(qhelptr);
     }
 
     m_helpManager = new LocalHelpManager(this);
@@ -448,9 +448,9 @@ void HelpPlugin::modeChanged(Core::Id mode, Core::Id old)
 {
     Q_UNUSED(old)
     if (mode == m_mode->id()) {
-        qApp->setOverrideCursor(Qt::WaitCursor);
+        QGuiApplication::setOverrideCursor(Qt::WaitCursor);
         doSetupIfNeeded();
-        qApp->restoreOverrideCursor();
+        QGuiApplication::restoreOverrideCursor();
     }
 }
 

src/plugins/help/helpviewer.cpp

@@ -35,7 +35,7 @@
 #include <QFileInfo>
 #include <QUrl>
 
-#include <QApplication>
+#include <QGuiApplication>
 #include <QDesktopServices>
 #include <QMouseEvent>
 
@@ -156,12 +156,12 @@ void HelpViewer::home()
 
 void HelpViewer::slotLoadStarted()
 {
-    qApp->setOverrideCursor(QCursor(Qt::WaitCursor));
+    QGuiApplication::setOverrideCursor(QCursor(Qt::WaitCursor));
 }
 
 void HelpViewer::slotLoadFinished()
 {
-    qApp->restoreOverrideCursor();
+    QGuiApplication::restoreOverrideCursor();
     emit sourceChanged(source());
     emit loadFinished();
 }

src/plugins/help/searchwidget.cpp

@@ -184,13 +184,13 @@ void SearchWidget::search() const
 
 void SearchWidget::searchingStarted()
 {
-    qApp->setOverrideCursor(QCursor(Qt::WaitCursor));
+    QGuiApplication::setOverrideCursor(QCursor(Qt::WaitCursor));
 }
 
 void SearchWidget::searchingFinished(int hits)
 {
     Q_UNUSED(hits)
-    qApp->restoreOverrideCursor();
+    QGuiApplication::restoreOverrideCursor();
 }
 
 void SearchWidget::indexingStarted()