qpa: Expose output names to QScreen

It can be useful for things such as effects.

plugins/qpa/screen.cpp

@@ -64,5 +64,10 @@ qreal Screen::devicePixelRatio() const
     return m_screen != -1 ? screens()->scale(m_screen) : 1.0;
 }
 
+QString Screen::name() const
+{
+    return m_screen != -1 ? screens()->name(m_screen) : QString();
+}
+
 }
 }

plugins/qpa/screen.h

@@ -24,6 +24,7 @@ public:
     explicit Screen(int screen);
     ~Screen() override;
 
+    QString name() const override;
     QRect geometry() const override;
     int depth() const override;
     QImage::Format format() const override;