Add some mechanism to help screenshot creation

If QTC_SCREENSHOTS_PATH points to a writable directory, each widget that
has been registered with ICore's setupScreenShooter(const QString &name,
QWidget *w) will dump a screen shot to this directory as soon as the
widget is shown.

Change-Id: I2dec12064f1bb3c510d2fd9d27c1b79f7b7d5f30
Reviewed-by: Jake Petroules <jake.petroules@qt.io>

src/plugins/coreplugin/icore.h

@@ -29,6 +29,7 @@
 #include "id.h"
 
 #include <QObject>
+#include <QRect>
 #include <QSettings>
 
 #include <functional>
@@ -130,6 +131,7 @@ public:
     static void addPreCloseListener(const std::function<bool()> &listener);
 
     static QString systemInformation();
+    static void setupScreenShooter(const QString &name, QWidget *w, const QRect &rc = QRect());
 
 public slots:
     static void saveSettings();