Replace 0 with nullptr

So if people are using the -Wzero-as-null-pointer-constant don't get a warning when using these private QPA includes

Change-Id: I6deb089b17a844680db24998d60c94de7a1227b1
Reviewed-by: David Faure <david.faure@kdab.com>
Reviewed-by: Jesus Fernandez <Jesus.Fernandez@qt.io>

src/gui/kernel/qinputdevicemanager_p.h

@@ -72,7 +72,7 @@ public:
         DeviceTypeTablet
     };
 
-    QInputDeviceManager(QObject *parent = 0);
+    QInputDeviceManager(QObject *parent = nullptr);
 
     int deviceCount(DeviceType type) const;
 

src/gui/kernel/qplatforminputcontextplugin_p.h

@@ -66,7 +66,7 @@ class Q_GUI_EXPORT QPlatformInputContextPlugin : public QObject
 {
     Q_OBJECT
 public:
-    explicit QPlatformInputContextPlugin(QObject *parent = 0);
+    explicit QPlatformInputContextPlugin(QObject *parent = nullptr);
     ~QPlatformInputContextPlugin();
 
     virtual QPlatformInputContext *create(const QString &key, const QStringList &paramList) = 0;

src/gui/kernel/qplatformintegrationplugin.h

@@ -64,7 +64,7 @@ class Q_GUI_EXPORT QPlatformIntegrationPlugin : public QObject
 {
     Q_OBJECT
 public:
-    explicit QPlatformIntegrationPlugin(QObject *parent = 0);
+    explicit QPlatformIntegrationPlugin(QObject *parent = nullptr);
     ~QPlatformIntegrationPlugin();
 
     virtual QPlatformIntegration *create(const QString &key, const QStringList &paramList);

src/gui/kernel/qplatformsharedgraphicscache.h

@@ -69,7 +69,7 @@ public:
         OpenGLTexture
     };
 
-    explicit QPlatformSharedGraphicsCache(QObject *parent = 0) : QObject(parent) {}
+    explicit QPlatformSharedGraphicsCache(QObject *parent = nullptr) : QObject(parent) {}
 
     virtual void beginRequestBatch() = 0;
     virtual void ensureCacheInitialized(const QByteArray &cacheId, BufferType bufferType,

src/gui/kernel/qplatformthemeplugin.h

@@ -63,7 +63,7 @@ class Q_GUI_EXPORT QPlatformThemePlugin : public QObject
 {
     Q_OBJECT
 public:
-    explicit QPlatformThemePlugin(QObject *parent = 0);
+    explicit QPlatformThemePlugin(QObject *parent = nullptr);
     ~QPlatformThemePlugin();
 
     virtual QPlatformTheme *create(const QString &key, const QStringList &paramList) = 0;