Examples: Do not depend on transitive includes

Change-Id: I7bba855a14289edbedbaa07a1234213f59085c1d
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>

examples/corelib/serialization/convert/converter.h

@@ -54,6 +54,7 @@
 #include <QIODevice>
 #include <QPair>
 #include <QVariant>
+#include <QVariantMap>
 #include <QList>
 
 class VariantOrderedMap : public QList<QPair<QVariant, QVariant>>

examples/opengl/contextinfo/widget.cpp

@@ -57,6 +57,8 @@
 #include <QCheckBox>
 #include <QHBoxLayout>
 #include <QLabel>
+#include <QList>
+#include <QByteArray>
 #include <QPushButton>
 #include <QTextEdit>
 #include <QSplitter>

examples/widgets/mainwindows/mainwindow/mainwindow.h

@@ -52,6 +52,9 @@
 #define MAINWINDOW_H
 
 #include <QMainWindow>
+#include <QMap>
+#include <QString>
+#include <QSize>
 
 class ToolBar;
 QT_FORWARD_DECLARE_CLASS(QMenu)

examples/widgets/painting/fontsampler/mainwindow.h

@@ -56,6 +56,11 @@
 #if defined(QT_PRINTSUPPORT_LIB)
 #include <QtPrintSupport/qtprintsupportglobal.h>
 #endif
+
+#include <QList>
+#include <QMap>
+#include <QString>
+
 QT_BEGIN_NAMESPACE
 class QPrinter;
 class QTextEdit;